Blackrock Bond Fund N-CSRS Certified semi-annual shareholder report (management investment company)

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM N-CSR

CERTIFIED SHAREHOLDER REPORT OF REGISTERED MANAGEMENT INVESTMENT COMPANIES

Investment Company Act file number: 811-02857 and 811-21434

Name of Fund: BlackRock Total Return Fund of BlackRock Bond Fund, Inc. and Master Total Return Portfolio of Master Bond LLC

Fund Address:    100 Bellevue Parkway, Wilmington, DE 19809

Name and address of agent for service: John M. Perlowski, Chief Executive Officer, BlackRock Total Return Fund of BlackRock Bond Fund, Inc. and Master Total Return Portfolio of Master Bond LLC, 55 East 52^nd Street, New York, NY 10055

Registrants’ telephone number, including area code: (800) 441-7762

Date of fiscal year end: 09/30/2021

Date of reporting period: 03/31/2021

Item 1 – Report to Stockholders

(a) The Report to Shareholders is attached herewith.

MARCH 31, 2021

2021 Semi-Annual Report

(Unaudited)

BlackRock Bond Fund, Inc.

· BlackRock Total Return Fund

Not FDIC Insured • May Lose Value • No Bank Guarantee

The Markets in Review

Dear Shareholder,

The 12-month reporting period as of March 31, 2021 reflected a remarkable period of disruption and adaptation, as the global economy dealt with the implications of the coronavirus (or “COVID-19”) pandemic. As the period began, the response to the virus’s spread was well underway, and countries around the world instituted economically disruptive countermeasures. Stay-at-home orders and closures of non-essential businesses became widespread, many workers were laid off, and unemployment claims spiked, causing a global recession and a sharp fall in equity prices.

As April 2020 began, stocks were near their lowest point since the beginning of the pandemic. However, a steady recovery began, as businesses started re-opening and governments learned to adapt to life with the virus. Equity prices continued to rise throughout the summer, fed by strong fiscal and monetary support and improving economic indicators. Many equity indices neared or surpassed all-time highs late in the reporting period following the implementation of mass vaccination campaigns and passage of an additional $1.9 trillion of fiscal stimulus. In the United States, both large- and small-capitalization stocks posted a significant advance. International equities also gained, as both developed countries and emerging markets rebounded substantially.

The 10-year U.S. Treasury yield (which is inversely related to bond prices) was near all-time lows as the period began, reflecting a reduced investor appetite for risk. However, inflation concerns from a rapidly expanding economy raised yields late in the reporting period, leading to a negative overall return for most U.S. Treasuries. In the corporate bond market, support from the U.S. Federal Reserve (the “Fed”) assuaged credit concerns and led to positive returns for corporate bonds, particularly high-yield corporates, which gained substantially.

The Fed remained committed to accommodative monetary policy by maintaining near zero interest rates and by announcing that inflation could exceed its 2% target for a sustained period without triggering a rate increase. To stabilize credit markets, the Fed also continued purchasing significant quantities of bonds, as did other influential central banks around the world, including the European Central Bank and the Bank of Japan.

Looking ahead, while coronavirus-related disruptions have clearly hindered worldwide economic growth, we believe that the global expansion will continue to accelerate as vaccination efforts ramp up and pent-up consumer demand leads to higher spending. In early 2021, President Biden signed one of the largest economic rescue packages in U.S. history, which should provide a solid tailwind for economic growth. In our view, inflation is likely to increase somewhat as the expansion continues, but moderate inflation is less likely to be followed by interest rate hikes that could threaten the economic expansion due to the change in Fed policy.

Overall, we favor a positive stance toward risk, with an overweight in equities. We see U.S. and Asian equities outside of Japan benefiting from structural growth trends in technology, while emerging markets should be particularly helped by a vaccine-led economic expansion. While we are neutral overall on credit, rising inflation should provide tailwinds for inflation-protected bonds, and global high-yield and Asian bonds also present attractive opportunities. We believe that international diversification and a focus on sustainability can help provide portfolio resilience, and the disruption created by the coronavirus appears to be accelerating the shift toward sustainable investments.

In this environment, our view is that investors need to think globally, extend their scope across a broad array of asset classes, and be nimble as market conditions change. We encourage you to talk with your financial advisor and visit blackrock.com for further insight about investing in today’s markets.

Sincerely,

Rob Kapito

President, BlackRock Advisors, LLC

Rob Kapito

President, BlackRock Advisors, LLC

Total Returns as of March 31, 2021
	6-Month	12-Month
U.S. large cap equities (S&P 500® Index)	19.07%	56.35%
U.S. small cap equities (Russell 2000® Index)	48.05	94.85
International equities (MSCI Europe, Australasia, Far East Index)	20.08	44.57
Emerging market equities (MSCI Emerging Markets Index)	22.43	58.39
3-month Treasury bills (ICE BofA 3-Month U.S. Treasury Bill Index)	0.06	0.12
U.S. Treasury securities (ICE BofA 10-Year U.S. Treasury Index)	(8.88)	(8.23)
U.S. investment grade bonds (Bloomberg Barclays U.S. Aggregate Bond Index)	(2.73)	0.71
Tax-exempt municipal bonds (S&P Municipal Bond Index)	1.46	5.29
U.S. high yield bonds (Bloomberg Barclays U.S. Corporate High Yield 2% Issuer Capped Index)	7.35	23.65
Past performance is not an indication of future results. Index performance is shown for illustrative purposes only. You cannot invest directly in an index.

2 THIS   PAGE   IS   NOT   PART   OF   YOUR   FUND   REPORT

Table of Contents

	Page
The Markets in Review		2
Semi-Annual Report:
Fund Summary		4
About Fund Performance		7
Disclosure of Expenses		7
Derivative Financial Instruments		8
Fund Financial Statements:
Statement of Assets and Liabilities		9
Statement of Operations		11
Statements of Changes in Net Assets		12
Fund Financial Highlights		13
Fund Notes to Financial Statements		20
Master Portfolio Information		25
Master Portfolio Financial Statements:
Schedule of Investments		26
Statement of Assets and Liabilities		97
Statement of Operations		99
Statements of Changes in Net Assets		100
Master Portfolio Financial Highlights		101
Master Portfolio Notes to Financial Statements		102
Statement Regarding Liquidity Risk Management Program		116
Additional Information		117
Glossary of Terms Used in this Report		119

3

Fund Summary as of March 31, 2021  BlackRock Total Return Fund

Investment Objective

BlackRock Total Return Fund’s (the “Fund”) investment objective is to realize a total return that exceeds that of the Bloomberg Barclays U.S. Aggregate Bond Index.

Portfolio Management Commentary

How did the Fund perform?

For the six-month period ended March 31, 2021, all of the Fund’s share classes outperformed its benchmark, the Bloomberg Barclays U.S. Aggregate Bond Index. The Fund invests all of its assets in Master Total Return Portfolio (the “Master Portfolio”).

What factors influenced performance?

The Master Portfolio’s high yield corporate bond holdings, active positioning with respect to duration (sensitivity to interest rate changes) and allocation to structured products contributed positively to relative performance during the period.

Conversely, the Master Portfolio’s positioning with respect to agency mortgage-backed securities (“MBS”) detracted from relative performance over the period, along with its U.S. investment grade corporate bond exposures.

The Master Portfolio held derivatives in the form of futures and forward contracts for risk management purposes as well as to manage exposures, with the goals of generating return and managing risk. The use of derivatives had a negative impact on the Fund’s performance during the period.

The Master Portfolio held a 6.4% cash position at period end. The investment adviser believes that Treasury securities are currently unattractive from a risk/reward perspective, which led the Master Portfolio to remain underweight duration versus the benchmark while also holding an elevated cash position. The Master Portfolio’s cash position did not have a material impact on the Fund’s performance during the period.

Describe recent portfolio activity.

Through the end of 2020, the Master Portfolio continued its slightly long duration stance, while mainly favoring the front end of the U.S. yield curve. As the European Central Bank delivered its monetary easing package, the Master Portfolio’s European sovereign debt exposure was increased. The Fund’s exposures included long German bunds as well as long positions in France and Italy interest rates. While the investment adviser continues to favor high quality “carry” assets (i.e., low risk, income-generating assets) in the portfolio, exposure to investment grade corporate credit was reduced given expensive valuations. In turn, the Master Portfolio added to agency MBS positions given robust demand and attractive relative value compared with other high-quality spread assets. Lastly, the Master Portfolio increased exposure to inflation-protected bonds that the investment adviser believes could benefit from a modest uptick in global growth.

At the start of 2021, the investment adviser began to shift the portfolio toward a slightly more “risk-on” tone, favoring structured products, a larger allocation to high-yield corporate credit, and emerging market debt. In addition, the investment adviser began to trim exposure to high-quality spread assets, including U.S. investment grade corporate credit and agency MBS given stretched valuations, while also reducing duration at the back end of the yield curve given the investment adviser’s outlook for higher U.S. interest rates. These changes were made in light of stronger-than-expected economic growth, additional fiscal stimulus and more robust consumer demand.

Describe portfolio positioning at period end.

At period end, the Master Portfolio maintained a duration underweight versus the benchmark, favoring European peripheral markets, high-quality emerging market debt and cash. In addition, the Master Portfolio was modestly underweight in agency MBS and slightly overweight in U.S. investment grade corporate bonds. The Master Portfolio emphasized income-oriented asset classes, including emerging market debt, U.S. high-yield corporate bonds, structured products, and both U.S. and non-U.S. investment grade corporate credit.

The views expressed reflect the opinions of BlackRock as of the date of this report and are subject to change based on changes in market, economic or other conditions. These views are not intended to be a forecast of future events and are no guarantee of future results.

4 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Fund Summary as of March 31, 2021 (continued) BlackRock Total Return Fund

Performance Summary for the Period Ended March 31, 2021

										Average Annual Total Returns(a)(b)
										1 Year						5 Years						10 Years
	Standardized 30 Day Yields			Unsubsidized 30 Day Yields			6-Month Total Returns			Without Sales Charge			With Sales Charge			Without Sales Charge			With Sales Charge			Without Sales Charge			With Sales Charge
Institutional		1.55	%		1.53	%		(0.83	)%		6.56	%		N/A			3.95	%		N/A			4.45	%		N/A
Service		1.24			1.19			(1.06	)		6.23			N/A			3.64			N/A			4.16			N/A
Investor A		1.22			1.21			(1.05	)		6.24			1.99	%		3.60			2.75	%		4.10			3.68	%
Investor A1		1.40			1.31			(0.99	)		6.41			N/A			3.78			N/A			4.30			N/A
Investor C		0.56			0.55			(1.41	)		5.50			4.50			2.91			2.91			3.57			3.57
Class K		1.63			1.62			(0.80	)		6.64			N/A			4.02			N/A			4.54			N/A
Class R		0.96			0.95			(1.20	)		5.85			N/A			3.33			N/A			3.84			N/A
Bloomberg Barclays U.S. Aggregate Bond Index(c)		—			—			(2.73	)		0.71			N/A			3.10			N/A			3.44			N/A

^(a)  Assuming maximum sales charges, if any. Average annual total returns with and without sales charges reflect reductions for distribution and service fees. See “About Fund Performance” for a detailed description of share classes, including any related sales charges and fees.

^(b)  The Fund invests all of its assets in the Master Portfolio. The Master Portfolio typically invests more than 90% of its assets in a diversified portfolio of fixed-income securities such as corporate bonds and notes, mortgage-backed securities, asset-backed securities, convertible securities, preferred securities and government obligations. Under normal circumstances, the Master Portfolio invests at least 80% of its assets in bonds and invests primarily in investment grade fixed income securities.

^(c)  A widely recognized unmanaged market-weighted index comprised of investment-grade corporate bonds rated BBB or better, mortgages and U.S. Treasury and U.S. Government agency issues with at least one year to maturity.

N/A - Not applicable as share class and index do not have a sales charge.

Past performance is not an indication of future results.

Performance results may include adjustments made for financial reporting purposes in accordance with U.S. generally accepted accounting principles.

FUND   SUMMARY 5

Fund Summary as of March 31, 2021 (continued) BlackRock Total Return Fund

Expense Example

	Actual							Hypothetical(a)
	Beginning		Ending		Expenses			Beginning		Ending		Expenses		Annualized
	Account Value		Account Value		Paid During			Account Value		Account Value		Paid During		Expense
		(10/01/20)		(03/31/21)		the Period	(b)		(10/01/20)		(03/31/21)		the Period		Ratio
Institutional		$ 1,000.00		$   991.70		$ 2.19			$ 1,000.00		$ 1,022.73		$ 2.22		0.44	%
Service		1,000.00		989.40		3.72			1,000.00		1,021.19		3.78		0.75
Investor A		1,000.00		989.50		3.61			1,000.00		1,021.30		3.67		0.73
Investor A1		1,000.00		990.10		2.93			1,000.00		1,021.98		2.98		0.59
Investor C		1,000.00		985.90		7.13			1,000.00		1,017.75		7.25		1.44
Class K		1,000.00		992.00		1.81			1,000.00		1,023.12		1.84		0.36
Class R		1,000.00		988.00		5.11			1,000.00		1,019.79		5.19		1.03

^(a)  Hypothetical 5% annual return before expenses is calculated by prorating the number of days in the most recent fiscal half year divided by 365.

^(b)  For each class of the Fund, expenses are equal to the annualized expense ratio for the class, multiplied by the average account value over the period, multiplied by 182/365 (to reflect the one-half year period shown). Because the Fund invests all of its assets in the Master Portfolio the expense example reflects the net expenses of both the Fund and the Master Portfolio in which it invests.

See “Disclosure of Expenses” for further information on how expenses were calculated.

6 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

About Fund Performance

Institutional and Class K Shares are not subject to any sales charge. These shares bear no ongoing distribution or service fees and are available only to certain eligible investors.

Service Shares are not subject to any sales charge. These shares are subject to a service fee of 0.25% per year (but no distribution fee) and are only available to certain eligible investors.

Investor A Shares are subject to a maximum initial sales charge (front-end load) of 4.00% and a service fee of 0.25% per year (but no distribution fee). Certain redemptions of these shares may be subject to a contingent deferred sales charge (“CDSC”) where no initial sales charge was paid at the time of purchase. These shares are generally available through financial intermediaries.

Investor A1 Shares are subject to a maximum initial sales charge (front-end load) of 1.00% and a service fee of 0.10% per year (but no distribution fee). The maximum initial sales charge does not apply to current eligible shareholders of Investor A1 Shares of the Fund. These shares are only available for dividend and capital gain reinvestment by existing shareholders and for purchase by certain eligible employer-sponsored retirement plans. Certain redemptions of these shares may be subject to a CDSC where no initial sales charge was paid at the time of purchase. However, the CDSC does not apply to redemptions by certain employer-sponsored retirement plans or to redemptions of shares acquired through the reinvestment of dividends and capital gains by existing shareholders.

Investor C Shares are subject to a 1.00% CDSC if redeemed within one year of purchase. In addition, these shares are subject to a distribution fee of 0.75% per year and a service fee of 0.25% per year. These shares are generally available through financial intermediaries. These shares automatically convert to Investor A Shares after approximately eight years.

Class R Shares are not subject to any sales charge. These shares are subject to a distribution fee of 0.25% per year and a service fee of 0.25% per year. These shares are available only to certain employer-sponsored retirement plans.

Past performance is not an indication of future results. Financial markets have experienced extreme volatility and trading in many instruments has been disrupted. These circumstances may continue for an extended period of time, and may continue to affect adversely the value and liquidity of the fund’s investments. As a result, current performance may be lower or higher than the performance data quoted. Refer to blackrock.com to obtain performance data current to the most recent month-end. Performance results do not reflect the deduction of taxes that a shareholder would pay on Fund distributions or the redemption of Fund shares. Figures shown in the performance tables on the previous page assume reinvestment of all distributions, if any, at NAV on the ex-dividend date or payable date, as applicable. Investment return and principal value of shares will fluctuate so that shares, when redeemed, may be worth more or less than their original cost. Distributions paid to each class of shares will vary because of the different levels of service, distribution and transfer agency fees applicable to each class, which are deducted from the income available to be paid to shareholders.

BlackRock Advisors, LLC (the “Manager”), the Fund’s investment adviser, has contractually and/or voluntarily agreed to waive and/or reimburse a portion of the Fund’s expenses. Without such waiver(s) and/or reimbursement(s), the Fund’s performance would have been lower. With respect to the Fund’s voluntary waiver(s), if any, the Manager is under no obligation to waive and/or reimburse or to continue waiving and/or reimbursing its fees and such voluntary waiver(s) may be reduced or discontinued at any time. With respect to the Fund’s contractual waiver(s), if any, the Manager is under no obligation to continue waiving and/or reimbursing its fees after the applicable termination date of such agreement. See the Notes to Financial Statements for additional information on waivers and/or reimbursements. The standardized 30-day yield includes the effects of any waivers and/or reimbursements. The unsubsidized 30-day yield excludes the effects of any waivers and/or reimbursements.

Disclosure of Expenses

Shareholders of the Fund may incur the following charges: (a) transactional expenses, such as sales charges; and (b) operating expenses, including administration fees, service and distribution fees, including 12b-1 fees, acquired fund fees and expenses, and other fund expenses. The expense example shown on the previous page (which is based on a hypothetical investment of $1,000 invested on October 1, 2020 and held through March 31, 2021) is intended to assist shareholders both in calculating expenses based on an investment in the Fund and in comparing these expenses with similar costs of investing in other mutual funds.

The expense example provides information about actual account values and actual expenses. In order to estimate the expenses a shareholder paid during the period covered by this report, shareholders can divide their account value by $1,000 and then multiply the result by the number corresponding to their share class under the heading entitled “Expenses Paid During the Period.”

The expense example also provides information about hypothetical account values and hypothetical expenses based on the Fund’s actual expense ratio and an assumed rate of return of 5% per year before expenses. In order to assist shareholders in comparing the ongoing expenses of investing in the Fund and other funds, compare the 5% hypothetical example with the 5% hypothetical examples that appear in shareholder reports of other funds.

The expenses shown in the expense example are intended to highlight shareholders’ ongoing costs only and do not reflect transactional expenses, such as sales charges, if any. Therefore, the hypothetical example is useful in comparing ongoing expenses only, and will not help shareholders determine the relative total expenses of owning different funds. If these transactional expenses were included, shareholder expenses would have been higher.

ABOUT   FUND   PERFORMANCE 7

Derivative Financial Instruments

The Master Portfolio may invest in various derivative financial instruments. These instruments are used to obtain exposure to a security, commodity, index, market, and/or other assets without owning or taking physical custody of securities, commodities and/or other referenced assets or to manage market, equity, credit, interest rate, foreign currency exchange rate, commodity and/or other risks. Derivative financial instruments may give rise to a form of economic leverage and involve risks, including the imperfect correlation between the value of a derivative financial instrument and the underlying asset, possible default of the counterparty to the transaction or illiquidity of the instrument. The Master Portfolio’s successful use of a derivative financial instrument depends on the investment adviser’s ability to predict pertinent market movements accurately, which cannot be assured. The use of these instruments may result in losses greater than if they had not been used, may limit the amount of appreciation the Master Portfolio can realize on an investment and/or may result in lower distributions paid to shareholders. The Master Portfolio’s investments in these instruments, if any, are discussed in detail in the Master Portfolio’s Notes to Financial Statements.

8 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Statement of Assets and Liabilities (unaudited)

March 31, 2021

	BlackRock Total Return Fund
ASSETS
Investments at value — Master Portfolio	$	19,884,346,927
Receivables:
Capital shares sold		65,992,319
From the Manager		117,041
Prepaid expenses		319,064
Total assets		19,950,775,351
LIABILITIES
Payables:
Capital shares redeemed		34,241,677
Contributions to the Master Portfolio		31,750,643
Income dividend distributions		5,698,822
Investment advisory fees		4,871,169
Officer’s fees		12,093
Other accrued expenses		2,186,304
Other affiliate fees		95,377
Service and distribution fees		624,587
Total liabilities		79,480,672
NET ASSETS	$	19,871,294,679
NET ASSETS CONSIST OF
Paid-in capital	$	19,920,890,258
Accumulated loss		(49,595,579	)
NET ASSETS	$	19,871,294,679

FINANCIAL   STATEMENTS 9

Statement of Assets and Liabilities (unaudited) (continued)

March 31, 2021

	BlackRock Total Return Fund
NET ASSET VALUE
Institutional
Net assets	$	9,490,525,710
Shares outstanding		802,368,282
Net asset value	$	11.83
Shares authorized		1 billion
Par value	$	0.10
Service
Net assets	$	54,190,707
Shares outstanding		4,580,738
Net asset value	$	11.83
Shares authorized		50 million
Par value	$	0.10
Investor A
Net assets	$	2,222,708,521
Shares outstanding		187,844,948
Net asset value	$	11.83
Shares authorized		450 million
Par value	$	0.10
Investor A1
Net assets	$	22,981,687
Shares outstanding		1,943,853
Net asset value	$	11.82
Shares authorized		50 million
Par value	$	0.10
Investor C
Net assets	$	118,349,509
Shares outstanding		10,010,079
Net asset value	$	11.82
Shares authorized		100 million
Par value	$	0.10
Class K
Net assets	$	7,879,318,840
Shares outstanding		666,240,699
Net asset value	$	11.83
Shares authorized		1 billion
Par value	$	0.10
Class R
Net assets	$	83,219,705
Shares outstanding		7,032,078
Net asset value	$	11.83
Shares authorized		250 million
Par value	$	0.10

See notes to financial statements.

10 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Statement of Operations (unaudited)

Six Months Ended March 31, 2021

	BlackRock Total Return Fund
INVESTMENT INCOME
Net investment income allocated from the Master Portfolio:
Dividends — unaffiliated	$	1,274,336
Dividends — affiliated		4,024,475
Interest — unaffiliated		234,897,824
Securities lending income — affiliated — net		289,505
Foreign taxes withheld		(926,391	)
Expenses		(6,252,915	)
Fees waived		235,359
Total investment income		233,542,193
FUND EXPENSES
Investment advisory		27,784,312
Transfer agent — class specific		6,389,139
Service and distribution — class specific		3,707,988
Registration		345,103
Professional		112,550
Printing and postage		72,885
Officer		13,913
Accounting services		3,491
Miscellaneous		19,100
Total expenses		38,448,481
Less:
Transfer agent fees waived and/or reimbursed — class specific		(982,671	)
Total expenses after fees waived and/or reimbursed		37,465,810
Net investment income		196,076,383
REALIZED AND UNREALIZED GAIN (LOSS) ALLOCATED FROM THE MASTER PORTFOLIO
Net realized loss from investments, foreign currency transactions, forward foreign currency exchange contracts, futures contracts, options written and swaps		(71,893,343	)
Net change in unrealized appreciation (depreciation) on investments, foreign currency translations, forward foreign currency exchange contracts, futures contracts, options written, swaps and unfunded floating rate loan interests		(313,406,257	)
Total net realized and unrealized loss		(385,299,600	)
NET DECREASE IN NET ASSETS RESULTING FROM OPERATIONS	$	(189,223,217	)

See notes to financial statements.

FINANCIAL   STATEMENTS 11

Statements of Changes in Net Assets

	BlackRock Total Return Fund
	Six Months Ended 03/31/21 (unaudited)			Year Ended 09/30/20
INCREASE (DECREASE) IN NET ASSETS
OPERATIONS
Net investment income	$	196,076,383		$	389,646,148
Net realized gain (loss)		(71,893,343	)		783,160,459
Net change in unrealized appreciation (depreciation)		(313,406,257	)		35,540,690
Net increase (decrease) in net assets resulting from operations		(189,223,217	)		1,208,347,297
DISTRIBUTIONS TO SHAREHOLDERS
Institutional		(452,148,640	)		(197,028,390	)
Service		(2,508,833	)		(2,365,465	)
Investor A		(104,630,359	)		(41,081,533	)
Investor A1		(1,163,918	)		(543,852	)
Investor C		(5,784,595	)		(2,978,957	)
Investor C1		—			(17,662	)
Investor C2		—			(4,721	)
Class K		(355,097,279	)		(171,018,050	)
Class R		(3,964,894	)		(1,847,802	)
Decrease in net assets resulting from distributions to shareholders		(925,298,518	)		(416,886,432	)
CAPITAL SHARE TRANSACTIONS
Net increase in net assets derived from capital share transactions		1,972,281,864			3,326,092,408
NET ASSETS
Total increase in net assets		857,760,129			4,117,553,273
Beginning of period		19,013,534,550			14,895,981,277
End of period	$	19,871,294,679		$	19,013,534,550

See notes to financial statements.

12 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Financial Highlights

(For a share outstanding throughout each period)

	BlackRock Total Return Fund
	Institutional
	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Net asset value, beginning of period		$	12.53		$	11.95		$	11.21		$	11.77		$	11.96		$	11.71
Net investment income(a)			0.13			0.28			0.38			0.38			0.34			0.31
Net realized and unrealized gain (loss)			(0.22	)		0.60			0.75			(0.56	)		(0.18	)		0.32
Net increase (decrease) from investment operations			(0.09	)		0.88			1.13			(0.18	)		0.16			0.63
Distributions(b)
From net investment income			(0.14	)		(0.30	)		(0.39	)		(0.38	)		(0.35	)		(0.38	)
From net realized gain			(0.47	)		—			—			—			—			—
Total distributions			(0.61	)		(0.30	)		(0.39	)		(0.38	)		(0.35	)		(0.38	)
Net asset value, end of period		$	11.83		$	12.53		$	11.95		$	11.21		$	11.77		$	11.96
Total Return(c)
Based on net asset value			(0.83	)%(d)		7.51	%(e)		10.23	%		(1.55	)%(e)		1.43	%		5.47	%
Ratios to Average Net Assets(f)
Total expenses(g)			0.46	%(h)(i)		0.47	%(j)		0.47	%(j)		0.75	%(i)		0.74	%(i)		0.61	%(i)
Total expenses after fees waived and/or reimbursed(g)			0.44	%(h)(i)		0.44	%(j)		0.44	%(j)		0.71	%(i)		0.69	%(i)		0.58	%(i)
Total expenses after fees waived and/or reimbursed and excluding interest expense(g)			0.44	%(h)(i)		0.44	%(j)		0.44	%(j)		0.45	%(i)		0.45	%(i)		0.45	%(i)
Net investment income(g)			2.07	%(h)(i)		2.32	%(j)		3.33	%(j)		3.31	%(i)		2.93	%(i)		2.63	%(i)
Supplemental Data
Net assets, end of period (000)		$	9,490,526		$	9,067,527		$	6,535,538		$	5,402,121		$	4,621,641		$	3,126,440
Portfolio turnover rate of the Master Portfolio(k)			241	%		556	%		574	%		734	%		806	%		841	%

^(a) Based on average shares outstanding.

^(b) Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c) Where applicable, assumes the reinvestment of distributions.

^(d) Aggregate total return.

^(e) Includes a payment received from an affiliate, which had no impact on the Fund’s total return.

^(f) Includes the Fund’s share of the Master Portfolio’s allocated expenses and/or net investment income.

^(g) Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Investments in underlying funds			0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%

^(h) Annualized.

⁽ⁱ⁾ Includes the Fund’s share of the Master Portfolio’s allocated fees waived of less than 0.01%.

^(j) Includes the Fund’s share of the Master Portfolio’s allocated fees waived of 0.01%.

^(k) Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Portfolio turnover rate (excluding MDRs)			86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

FINANCIAL   HIGHLIGHTS 13

Financial Highlights  (continued)

(For a share outstanding throughout each period)

	BlackRock Total Return Fund (continued)
	Service
	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Net asset value, beginning of period		$	12.54		$	11.95		$	11.22		$	11.77		$	11.96		$	11.71
Net investment income(a)			0.11			0.26			0.35			0.34			0.31			0.28
Net realized and unrealized gain (loss)			(0.23	)		0.60			0.73			(0.54	)		(0.18	)		0.31
Net increase (decrease) from investment operations			(0.12	)		0.86			1.08			(0.20	)		0.13			0.59
Distributions(b)
From net investment income			(0.12	)		(0.27	)		(0.35	)		(0.35	)		(0.32	)		(0.34	)
From net realized gain			(0.47	)		—			—			—			—			—
Total distributions			(0.59	)		(0.27	)		(0.35	)		(0.35	)		(0.32	)		(0.34	)
Net asset value, end of period		$	11.83		$	12.54		$	11.95		$	11.22		$	11.77		$	11.96
Total Return(c)
Based on net asset value			(1.06	)%(d)		7.28	%(e)		9.80	%		(1.76	)%(e)		1.13	%		5.15	%
Ratios to Average Net Assets(f)
Total expenses(g)			0.72	%(h)(i)		0.74	%(j)		0.74	%(j)		1.03	%(i)		1.02	%(i)		0.93	%(i)
Total expenses after fees waived and/or reimbursed(g)			0.71	%(h)(i)		0.74	%(j)		0.74	%(j)		1.03	%(i)		1.00	%(i)		0.88	%(i)
Total expenses after fees waived and/or reimbursed and excluding interest expense(g)			0.75	%(h)(i)		0.74	%(j)		0.74	%(j)		0.75	%(i)		0.75	%(i)		0.75	%(i)
Net investment income(g)			1.80	%(h)(i)		2.15	%(j)		3.04	%(j)		3.01	%(i)		2.62	%(i)		2.35	%(i)
Supplemental Data
Net assets, end of period (000)		$	54,191		$	57,849		$	120,243		$	117,278		$	125,903		$	74,723
Portfolio turnover rate of the Master Portfolio(k)			241	%		556	%		574	%		734	%		806	%		841	%

^(a) Based on average shares outstanding.

^(b) Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c) Where applicable, assumes the reinvestment of distributions.

^(d) Aggregate total return.

^(e) Includes a payment received from an affiliate, which had no impact on the Fund’s total return.

^(f) Includes the Fund’s share of the Master Portfolio’s allocated expenses and/or net investment income.

^(g) Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Investments in underlying funds			0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%

^(h) Annualized.

⁽ⁱ⁾ Includes the Fund’s share of the Master Portfolio’s allocated fees waived of less than 0.01%.

^(j) Includes the Fund’s share of the Master Portfolio’s allocated fees waived of 0.01%.

^(k) Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Portfolio turnover rate (excluding MDRs)			86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

14 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Financial Highlights  (continued)

(For a share outstanding throughout each period)

	BlackRock Total Return Fund (continued)
	Investor A
	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Net asset value, beginning of period		$	12.54		$	11.96		$	11.22		$	11.78		$	11.96		$	11.71
Net investment income(a)			0.11			0.25			0.34			0.34			0.30			0.28
Net realized and unrealized gain (loss)			(0.23	)		0.60			0.75			(0.56	)		(0.16	)		0.31
Net increase (decrease) from investment operations			(0.12	)		0.85			1.09			(0.22	)		0.14			0.59
Distributions(b)
From net investment income			(0.12	)		(0.27	)		(0.35	)		(0.34	)		(0.32	)		(0.34	)
From net realized gain			(0.47	)		—			—			—			—			—
Total distributions			(0.59	)		(0.27	)		(0.35	)		(0.34	)		(0.32	)		(0.34	)
Net asset value, end of period		$	11.83		$	12.54		$	11.96		$	11.22		$	11.78		$	11.96
Total Return(c)
Based on net asset value			(1.05	)%(d)		7.16	%(e)		9.85	%		(1.88	)%(e)		1.18	%		5.12	%
Ratios to Average Net Assets(f)
Total expenses(g)			0.73	%(h)(i)		0.76	%(j)		0.79	%(j)		1.08	%(i)		1.04	%(i)		0.91	%(i)
Total expenses after fees waived and/or reimbursed(g)			0.73	%(h)(i)		0.76	%(j)		0.78	%(j)		1.07	%(i)		1.03	%(i)		0.91	%(i)
Total expenses after fees waived and/or reimbursed and excluding interest expense(g)			0.73	%(h)(i)		0.76	%(j)		0.78	%(j)		0.79	%(i)		0.79	%(i)		0.78	%(i)
Net investment income(g)			1.78	%(h)(i)		2.02	%(j)		3.00	%(j)		2.97	%(i)		2.58	%(i)		2.34	%(i)
Supplemental Data
Net assets, end of period (000)		$	2,222,709		$	2,147,025		$	1,840,587		$	1,729,459		$	2,033,975		$	2,087,043
Portfolio turnover rate of the Master Portfolio(k)			241	%		556	%		574	%		734	%		806	%		841	%

^(a) Based on average shares outstanding.

^(b) Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c) Where applicable, excludes the effects of any sales charges and assumes the reinvestment of distributions.

^(d) Aggregate total return.

^(e) Includes a payment received from an affiliate, which had no impact on the Fund’s total return.

^(f) Includes the Fund’s share of the Master Portfolio’s allocated expenses and/or net investment income.

^(g) Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Investments in underlying funds			0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%

^(h) Annualized.

⁽ⁱ⁾ Includes the Fund’s share of the Master Portfolio’s allocated fees waived of less than 0.01%.

^(j) Includes the Fund’s share of the Master Portfolio’s allocated fees waived of 0.01%.

^(k) Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Portfolio turnover rate (excluding MDRs)			86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

FINANCIAL   HIGHLIGHTS 15

Financial Highlights  (continued)

(For a share outstanding throughout each period)

	BlackRock Total Return Fund (continued)
	Investor A1
	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Net asset value, beginning of period		$	12.53		$	11.95		$	11.21		$	11.77		$	11.95		$	11.70
Net investment income(a)			0.13			0.27			0.37			0.36			0.32			0.30
Net realized and unrealized gain (loss)			(0.24	)		0.60			0.74			(0.56	)		(0.16	)		0.31
Net increase (decrease) from investment operations			(0.11	)		0.87			1.11			(0.20	)		0.16			0.61
Distributions(b)
From net investment income			(0.13	)		(0.29	)		(0.37	)		(0.36	)		(0.34	)		(0.36	)
From net realized gain			(0.47	)		—			—			—			—			—
Total distributions			(0.60	)		(0.29	)		(0.37	)		(0.36	)		(0.34	)		(0.36	)
Net asset value, end of period		$	11.82		$	12.53		$	11.95		$	11.21		$	11.77		$	11.95
Total Return(c)
Based on net asset value			(0.99	)%(d)		7.35	%(e)		10.06	%		(1.69	)%(e)		1.37	%		5.32	%
Ratios to Average Net Assets(f)
Total expenses(g)			0.56	%(h)(i)		0.61	%(j)		0.63	%(i)		0.92	%(i)		0.86	%(i)		0.74	%(i)
Total expenses after fees waived and/or reimbursed(g)			0.49	%(h)(i)		0.59	%(j)		0.59	%(i)		0.88	%(i)		0.84	%(i)		0.72	%(i)
Total expenses after fees waived and/or reimbursed and excluding interest expense(g)			0.59	%(h)(i)		0.59	%(j)		0.59	%(i)		0.60	%(i)		0.60	%(i)		0.60	%(i)
Net investment income(g)			2.02	%(h)(i)		2.22	%(j)		3.20	%(i)		3.17	%(i)		2.77	%(i)		2.54	%(i)
Supplemental Data
Net assets, end of period (000)		$	22,982		$	24,443		$	28,769		$	28,072		$	31,705		$	34,722
Portfolio turnover rate of the Master Portfolio(k)			241	%		556	%		574	%		734	%		806	%		841	%

^(a) Based on average shares outstanding.

^(b) Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c) Where applicable, excludes the effects of any sales charges and assumes the reinvestment of distributions.

^(d) Aggregate total return.

^(e) Includes a payment received from an affiliate, which had no impact on the Fund’s total return.

^(f) Includes the Fund’s share of the Master Portfolio’s allocated expenses and/or net investment income.

^(g) Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Investments in underlying funds			0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%

^(h) Annualized.

⁽ⁱ⁾ Includes the Fund’s share of the Master Portfolio’s allocated fees waived of less than 0.01%.

^(j) Includes the Fund’s share of the Master Portfolio’s allocated fees waived of 0.01%.

^(k) Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Portfolio turnover rate (excluding MDRs)			86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

16 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Financial Highlights  (continued)

(For a share outstanding throughout each period)

	BlackRock Total Return Fund (continued)
	Investor C
	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Net asset value, beginning of period		$	12.53		$	11.95		$	11.21		$	11.77		$	11.95		$	11.70
Net investment income(a)			0.08			0.16			0.27			0.27			0.22			0.20
Net realized and unrealized gain (loss)			(0.24	)		0.60			0.74			(0.56	)		(0.16	)		0.31
Net increase (decrease) from investment operations			(0.16	)		0.76			1.01			(0.29	)		0.06			0.51
Distributions(b)
From net investment income			(0.08	)		(0.18	)		(0.27	)		(0.27	)		(0.24	)		(0.26	)
From net realized gain			(0.47	)		—			—			—			—			—
Total distributions			(0.55	)		(0.18	)		(0.27	)		(0.27	)		(0.24	)		(0.26	)
Net asset value, end of period		$	11.82		$	12.53		$	11.95		$	11.21		$	11.77		$	11.95
Total Return(c)
Based on net asset value			(1.41	)%(d)		6.44	%(e)		9.14	%		(2.53	)%(e)		0.52	%		4.42	%
Ratios to Average Net Assets(f)
Total expenses(g)			1.45	%(h)(i)		1.49	%(j)		1.51	%(j)		1.82	%(i)		1.76	%(i)		1.66	%(i)
Total expenses after fees waived and/or reimbursed(g)			1.42	%(h)(i)		1.44	%(j)		1.44	%(j)		1.74	%(i)		1.68	%(i)		1.58	%(i)
Total expenses after fees waived and/or reimbursed and excluding interest expense(g)			1.44	%(h)(i)		1.44	%(j)		1.44	%(j)		1.45	%(i)		1.45	%(i)		1.45	%(i)
Net investment income(g)			1.09	%(h)(i)		1.36	%(j)		2.35	%(j)		2.32	%(i)		1.90	%(i)		1.67	%(i)
Supplemental Data
Net assets, end of period (000)		$	118,350		$	140,034		$	209,532		$	235,682		$	339,329		$	498,254
Portfolio turnover rate of the Master Portfolio(k)			241	%		556	%		574	%		734	%		806	%		841	%

^(a) Based on average shares outstanding.

^(b) Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c) Where applicable, excludes the effects of any sales charges and assumes the reinvestment of distributions.

^(d) Aggregate total return.

^(e) Includes a payment received from an affiliate, which had no impact on the Fund’s total return.

^(f) Includes the Fund’s share of the Master Portfolio’s allocated expenses and/or net investment income.

^(g) Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Investments in underlying funds			0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%

^(h) Annualized.

⁽ⁱ⁾ Includes the Fund’s share of the Master Portfolio’s allocated fees waived of less than 0.01%.

^(j) Includes the Fund’s share of the Master Portfolio’s allocated fees waived of 0.01%.

^(k) Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Portfolio turnover rate (excluding MDRs)			86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

FINANCIAL   HIGHLIGHTS 17

Financial Highlights  (continued)

(For a share outstanding throughout each period)

	BlackRock Total Return Fund (continued)
	Class K
	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Net asset value, beginning of period		$	12.53		$	11.95		$	11.21		$	11.77		$	11.95		$	11.71
Net investment income(a)			0.13			0.29			0.39			0.39			0.35			0.32
Net realized and unrealized gain (loss)			(0.22	)		0.60			0.74			(0.56	)		(0.17	)		0.30
Net increase (decrease) from investment operations			(0.09	)		0.89			1.13			(0.17	)		0.18			0.62
Distributions(b)
From net investment income			(0.14	)		(0.31	)		(0.39	)		(0.39	)		(0.36	)		(0.38	)
From net realized gain			(0.47	)		—			—			—			—			—
Total distributions			(0.61	)		(0.31	)		(0.39	)		(0.39	)		(0.36	)		(0.38	)
Net asset value, end of period		$	11.83		$	12.53		$	11.95		$	11.21		$	11.77		$	11.95
Total Return(c)
Based on net asset value			(0.80	)%(d)		7.59	%(e)		10.30	%		(1.49	)%(e)		1.59	%		5.44	%
Ratios to Average Net Assets(f)
Total expenses(g)			0.36	%(h)(i)		0.37	%(j)		0.37	%(j)		0.64	%(i)		0.64	%(i)		0.52	%(i)
Total expenses after fees waived and/or reimbursed(g)			0.36	%(h)(i)		0.37	%(j)		0.37	%(j)		0.64	%(i)		0.63	%(i)		0.52	%(i)
Total expenses after fees waived and/or reimbursed and excluding interest expense(g)			0.36	%(h)(i)		0.37	%(j)		0.37	%(j)		0.38	%(i)		0.39	%(i)		0.39	%(i)
Net investment income(g)			2.14	%(h)(i)		2.41	%(j)		3.40	%(j)		3.36	%(i)		3.00	%(i)		2.73	%(i)
Supplemental Data
Net assets, end of period (000)		$	7,879,319		$	7,491,107		$	6,015,062		$	4,726,240		$	3,751,146		$	2,770,095
Portfolio turnover rate of the Master Portfolio(k)			241	%		556	%		574	%		734	%		806	%		841	%

^(a) Based on average shares outstanding.

^(b) Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c) Where applicable, assumes the reinvestment of distributions.

^(d) Aggregate total return.

^(e) Includes a payment received from an affiliate, which had no impact on the Fund’s total return.

^(f) Includes the Fund’s share of the Master Portfolio’s allocated expenses and/or net investment income.

^(g) Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Investments in underlying funds			0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%

^(h) Annualized.

⁽ⁱ⁾ Includes the Fund’s share of the Master Portfolio’s allocated fees waived of less than 0.01%.

^(j) Includes the Fund’s share of the Master Portfolio’s allocated fees waived of 0.01%.

^(k) Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Portfolio turnover rate (excluding MDRs)			86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

18 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Financial Highlights  (continued)

(For a share outstanding throughout each period)

	BlackRock Total Return Fund (continued)
	Class R
	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Net asset value, beginning of period		$	12.54		$	11.96		$	11.22		$	11.78		$	11.96		$	11.71
Net investment income(a)			0.09			0.22			0.32			0.31			0.28			0.24
Net realized and unrealized gain (loss)			(0.23	)		0.59			0.74			(0.56	)		(0.17	)		0.32
Net increase (decrease) from investment operations			(0.14	)		0.81			1.06			(0.25	)		0.11			0.56
Distributions(b)
From net investment income			(0.10	)		(0.23	)		(0.32	)		(0.31	)		(0.29	)		(0.31	)
From net realized gain			(0.47	)		—			—			—			—			—
Total distributions			(0.57	)		(0.23	)		(0.32	)		(0.31	)		(0.29	)		(0.31	)
Net asset value, end of period		$	11.83		$	12.54		$	11.96		$	11.22		$	11.78		$	11.96
Total Return(c)
Based on net asset value			(1.20	)%(d)		6.88	%(e)		9.58	%		(2.12	)%(e)		0.93	%		4.86	%
Ratios to Average Net Assets(f)
Total expenses(g)			1.02	%(h)(i)		1.04	%(j)		1.07	%(i)		1.37	%(i)		1.34	%(i)		1.22	%(i)
Total expenses after fees waived and/or reimbursed(g)			1.00	%(h)(i)		1.03	%(j)		1.03	%(i)		1.31	%(i)		1.29	%(i)		1.17	%(i)
Total expenses after fees waived and/or reimbursed and excluding interest expense(g)			1.03	%(h)(i)		1.03	%(j)		1.03	%(i)		1.04	%(i)		1.04	%(i)		1.04	%(i)
Net investment income(g)			1.51	%(h)(i)		1.80	%(j)		2.76	%(i)		2.72	%(i)		2.36	%(i)		2.06	%(i)
Supplemental Data
Net assets, end of period (000)		$	83,220		$	85,550		$	142,718		$	156,009		$	160,166		$	90,332
Portfolio turnover rate of the Master Portfolio(k)			241	%		556	%		574	%		734	%		806	%		841	%

^(a)  Based on average shares outstanding.

^(b)  Distributions for annual periods determined in accordance with U.S. federal income tax regulations.

^(c)  Where applicable, assumes the reinvestment of distributions.

^(d)  Aggregate total return.

^(e)  Includes a payment received from an affiliate, which had no impact on the Fund’s total return.

^(f)  Includes the Fund’s share of the Master Portfolio’s allocated expenses and/or net investment income.

^(g)  Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Investments in underlying funds			0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%

^(h)  Annualized.

⁽ⁱ⁾  Includes the Fund’s share of the Master Portfolio’s allocated fees waived of less than 0.01%.

^(j) Includes the Fund’s share of the Master Portfolio’s allocated fees waived of 0.01%.

^(k)  Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:

	Six Months Ended
		03/31/21			Year Ended September 30,
		(unaudited)			2020			2019			2018			2017			2016
Portfolio turnover rate (excluding MDRs)			86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

FINANCIAL   HIGHLIGHTS 19

Notes to Financial Statements (unaudited)

1. ORGANIZATION

BlackRock Total Return Fund (the “Fund”), a series of BlackRock Bond Fund, Inc. (the “Corporation”), is registered under the Investment Company Act of 1940, as amended (the “1940 Act”), as an open-end management investment company. The Fund is classified as diversified. The Fund seeks to achieve its investment objective by investing all of its assets in Master Total Return Portfolio (the “Master Portfolio”) of Master Bond LLC, an affiliate of the Fund, which has the same investment objective and strategies as the Fund. The Corporation is organized as a Maryland corporation. The Master Bond LLC is organized as a Delaware limited liability company. The value of the Fund’s investment in the Master Portfolio reflects the Fund’s proportionate interest in the net assets of the Master Portfolio. The performance of the Fund is directly affected by the performance of the Master Portfolio. At March 31, 2021, the percentage of the Master Portfolio owned by the Fund was 94.4%. The financial statements of the Master Portfolio, including the Schedule of Investments, are included elsewhere in this report and should be read in conjunction with the Fund’s financial statements.

The Fund offers multiple classes of shares. All classes of shares have identical voting, dividend, liquidation and other rights and are subject to the same terms and conditions, except that certain classes bear expenses related to the shareholder servicing and distribution of such shares. Institutional, Service and Class K Shares are sold only to certain eligible investors. Class R Shares are sold only to certain employer-sponsored retirement plans. Service, Investor A, Investor A1, Investor C and Class R Shares bear certain expenses related to shareholder servicing of such shares, and Investor C and Class R Shares also bear certain expenses related to the distribution of such shares. Investor A and Investor C Shares are generally available through financial intermediaries. Investor A1 Shares are only available for dividend and capital gain reinvestment by existing shareholders, and for purchase by certain employer-sponsored retirement plans. Each class has exclusive voting rights with respect to matters relating to its shareholder servicing and distribution expenditures (except that Investor C shareholders may vote on material changes to the Investor A Shares distribution and service plan).

The Board of Directors of the Corporation and Board of Directors of the Master Bond LLC are referred to throughout this report as the “Board of Directors” or the “Board” and the members are referred to as “Directors”.

Share Class	Initial Sales Charge			CDSC			Conversion Privilege
Institutional, Service, Class K and Class R Shares		No			No		None
Investor A Shares		Yes			No	(a)	None
Investor A1 Shares		No	(b)		No	(c)	None
Investor C Shares		No			Yes	(d)	To Investor A Shares after approximately 8 years

^(a)  Investor A Shares may be subject to a contingent deferred sales charge (“CDSC”) where no initial sales charge was paid at the time of purchase.

^(b)  Investor A1 Shares are subject to a maximum sales charge on purchases of 1.00%. The sales charge does not apply to dividend and capital gain reinvestments by existing shareholders and new purchases for certain employer-sponsored retirement plans, which are currently the only investors who may invest in Investor A1 Shares.

^(c)  Investor A1 Shares may be subject to a CDSC for certain redemptions where no initial sales charge was paid at the time of purchase. However, the CDSC does not apply to redemptions by certain employer-sponsored retirement plans, or to redemptions of shares acquired through reinvestment of dividends and capital gains by existing shareholders.

^(d)  A CDSC of 1.00% is assessed on certain redemptions of Investor C Shares made within one year of after purchase.

The Fund, together with certain other registered investment companies advised by BlackRock Advisors, LLC (the “Manager”) or its affiliates, is included in a complex of non-index fixed-income mutual funds and all BlackRock-advised closed-end funds referred to as the BlackRock Fixed-Income Complex.

2. SIGNIFICANT ACCOUNTING POLICIES

The financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”), which may require management to make estimates and assumptions that affect the reported amounts of assets and liabilities in the financial statements, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of increases and decreases in net assets from operations during the reporting period. Actual results could differ from those estimates. The Fund is considered an investment company under U.S. GAAP and follows the accounting and reporting guidance applicable to investment companies. Below is a summary of significant accounting policies:

Investment Transactions and Income Recognition: For financial reporting purposes, contributions to and withdrawals from the Master Portfolio are accounted for on a trade date basis. The Fund records its proportionate share of the Master Portfolio’s income, expenses and realized and unrealized gains and losses on a daily basis. Realized and unrealized gains and losses are adjusted utilizing partnership tax allocation rules. In addition, the Fund accrues its own expenses. Income, expenses and realized and unrealized gains and losses are allocated daily to each class based on its relative net assets.

Distributions: Distributions from net investment income are declared daily and paid monthly. Distributions of capital gains are recorded on the ex-dividend dates and made at least annually. The character and timing of distributions are determined in accordance with U.S. federal income tax regulations, which may differ from U.S. GAAP.

Deferred Compensation Plan: Under the Deferred Compensation Plan (the “Plan”) approved by the Corporation’s Board, the directors who are not “interested persons” of the Fund, as defined in the 1940 Act (“Independent Directors”), may defer a portion of their annual complex-wide compensation. Deferred amounts earn an approximate return as though equivalent dollar amounts had been invested in common shares of certain funds in the BlackRock Fixed-Income Complex selected by the Independent Directors. This has the same economic effect for the Independent Directors as if the Independent Directors had invested the deferred amounts directly in certain funds in the BlackRock Fixed-Income Complex.

The Plan is not funded and obligations thereunder represent general unsecured claims against the general assets of the Fund, as applicable. Deferred compensation liabilities, if any, are included in the Directors’ and Officer’s fees payable in the Statement of Assets and Liabilities and will remain as a liability of the Fund until such amounts are distributed in accordance with the Plan.

Indemnifications: In the normal course of business, the Fund enters into contracts that contain a variety of representations that provide general indemnification. The Fund’s maximum exposure under these arrangements is unknown because it involves future potential claims against the Fund, which cannot be predicted with any certainty.

20 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Notes to Financial Statements (unaudited) (continued)

Other: Expenses directly related to the Fund or its classes are charged to the Fund or the applicable class. Expenses directly related to the Fund and other shared expenses prorated to the Fund are allocated daily to each class based on its relative net assets or other appropriate methods. Other operating expenses shared by several funds, including other funds managed by the Manager, are prorated among those funds on the basis of relative net assets or other appropriate methods.

The Fund has an arrangement with its custodian whereby credits are earned on uninvested cash balances, which could be used to reduce custody fees and/or overdraft charges. The Fund may incur charges on overdrafts, subject to certain conditions.

3. INVESTMENT VALUATION AND FAIR VALUE MEASUREMENTS

The Fund’s policy is to value its financial instruments at fair value. The Fund records its investment in the Master Portfolio at fair value based on the Fund’s proportionate interest in the net assets of the Master Portfolio. Valuation of securities held by the Master Portfolio is discussed in Note 3 of the Master Portfolio’s Notes to Financial Statements, which are included elsewhere in this report.

4. INVESTMENT ADVISORY AGREEMENT AND OTHER TRANSACTIONS WITH AFFILIATES

Investment Advisory: The Corporation, on behalf of the Fund, entered into an Investment Advisory Agreement with the Manager, the Fund’s investment adviser and an indirect, wholly-owned subsidiary of BlackRock, Inc. (“BlackRock”), to provide investment advisory and administrative services. The Manager is responsible for the management of the Fund’s portfolio and provides the personnel, facilities, equipment and certain other services necessary to the operations of the Fund.

For such services, the Fund pays the Manager a monthly fee at an annual rate equal to the following percentages of the average daily value of the Fund’s net assets:

Average Daily Net Assets	Investment Advisory Fees(a)
First $250 million		0.32	%
$250 million — $500 million		0.31
$500 million — $750 million		0.30
Greater than $750 million		0.29

^(a)  This investment advisory fee applies to the Fund for as long as the Fund invests in the Master Portfolio or another master fund advised by the Manager or an affiliate thereof in a master-feeder structure. If the Fund ceases to operate as a feeder fund in a master/feeder structure, the maximum actual investment advisory fees payable to the Manager (as a percentage of average daily net assets) by the Fund are as follows: 0.48% (first $250 million), 0.43% ($250 million - $500 million), 0.38% ($500 million - $750 million) and 0.34% (greater than $750 million).

With respect to the Fund, the Manager entered into separate sub-advisory agreements with BlackRock International Limited (“BIL”) and BlackRock (Singapore) Limited (“BRS”), each an affiliate of the Manager. The Manager pays BIL and BRS for services they provide for that portion of the Fund for which BIL and BRS, as applicable, act as sub-advisers, a monthly fee that is equal to a percentage of the investment advisory fees paid by the Fund to the Manager.

Service and Distribution Fees: The Trust, on behalf of the Corporation, on behalf of the Fund, entered into a Distribution Agreement and a Distribution and Service Plan with BlackRock Investments, LLC (“BRIL”), an affiliate of the Manager. Pursuant to the Distribution and Service Plan and in accordance with Rule 12b-1 under the 1940 Act, the Fund pays BRIL ongoing service and distribution fees. The fees are accrued daily and paid monthly at annual rates based upon the average daily net assets of the relevant share class of the Fund as follows:

Share Class	Service Fees			Distribution Fees
Service		0.25	%		N/A
Investor A		0.25			N/A
Investor A1		0.10			N/A
Investor C		0.25			0.75	%
Class R		0.25			0.25

BRIL and broker-dealers, pursuant to sub-agreements with BRIL, provide shareholder servicing and distribution services to the Fund. The ongoing service and/or distribution fee compensates BRIL and each broker-dealer for providing shareholder servicing and/or distribution related services to shareholders.

For the six months ended March 31, 2021, the following table shows the class specific service and distribution fees borne directly by each share class of the Fund:

	Service		Investor A		Investor A1		Investor C		Class R		Total
Service and distribution fees — class specific		$  67,768		$  2,760,654		$  11,993		$  653,909		$  213,664		$  3,707,988

Transfer Agent: Pursuant to written agreements, certain financial intermediaries, some of which may be affiliates, provide the Fund with sub-accounting, recordkeeping, sub-transfer agency and other administrative services with respect to servicing of underlying investor accounts. For these services, these entities receive an asset-based fee or an annual fee per shareholder account, which will vary depending on share class and/or net assets. For the six months ended March 31, 2021, the Fund paid $263,551 for the Fund’s Institutional Shares to affiliates of BlackRock in return for these services, which are included in transfer agent — class specific in the Statement of Operations.

NOTES   TO   FINANCIAL   STATEMENTS 21

Notes to Financial Statements (unaudited) (continued)

The Manager maintains a call center that is responsible for providing certain shareholder services to the Fund. Shareholder services include responding to inquiries and processing purchases and sales based upon instructions from shareholders. For the six months ended March 31, 2021, the Fund reimbursed the Manager the following amounts for costs incurred in running the call center, which are included in transfer agent — class specific in the Statement of Operations:

	Institutional		Service		Investor A		Investor A1		Investor C		Class K		Class R		Total
Reimbursed amounts		$  24,887		$  503		$  8,030		$  113		$  2,810		$  7,530		$ 860		$  44,733

For the six months ended March 31, 2021, the following table shows the class specific transfer agent fees borne directly by each share class of the Fund:

	Institutional		Service		Investor A		Investor A1		Investor C		Class K		Class R		Total
Transfer agent fees — class specific		$  4,715,214		$  44,731		$  1,309,030		$  22,525		$  65,254		$  157,031		$  75,354		$  6,389,139

Other Fees: For the six months ended March 31, 2021, affiliates earned underwriting discounts, direct commissions and dealer concessions on sales of the Fund’s Investor A Shares of $30,506.

For the six months ended March 31, 2021, affiliates received CDSCs as follows:

Share Class	Amounts
Investor A	$	16
Investor C		63,081
	$	63,097

Expense Limitations, Waivers and Reimbursements: With the exception of the Fund’s investment in the Master Portfolio, the Manager contractually agreed to waive its investment advisory fee with respect to any portion of the Fund’s assets invested in affiliated equity and fixed-income mutual funds and affiliated exchange-traded funds that have a contractual management fee through January 31, 2022. The contractual agreement may be terminated upon 90 days’ notice by a majority of the Independent Directors, or by a vote of a majority of the outstanding voting securities of the Fund. For the six months ended March 31, 2021, there were no fees waived by the Manager pursuant to this arrangement.

With respect to the Fund, the Manager contractually agreed to waive and/or reimburse fees or expenses in order to limit expenses, excluding interest expense, dividend expense, tax expense, acquired fund fees and expenses, and certain other fund expenses, which constitute extraordinary expenses not incurred in the ordinary course of the Fund’s business (“expense limitation”). The expense limitations as a percentage of average daily net assets are as follows:

Share Class	Expense Limitations
Institutional		0.44	%
Service		0.75
Investor A		0.78
Investor A1		0.59
Investor C		1.44
Class K		0.39
Class R		1.03

The Manager has agreed not to reduce or discontinue this contractual expense limitation through January 31, 2022, unless approved by the Board, including a majority of the Independent Directors, or by a vote of a majority of the outstanding voting securities of the Fund. For the six months ended March 31, 2021, there were no investment advisory fees waived and/or reimbursed by the Manager pursuant to this agreement.

In addition, these amounts waived and/or reimbursed by the Manager are included in transfer agent fees waived and/or reimbursed — class specific in the Statement of Operations. For the six months ended March 31, 2021, the class specific waivers and/or reimbursements are as follows:

	Institutional		Service		Investor A1		Investor C		Class R		Total
Transfer agent fees waived and/or reimbursed — class specific	$	957,482	$	6,313	$	6,817	$	10,056	$	2,003	$	982,671

Interfund Lending: In accordance with an exemptive order (the “Order”) from the U.S. Securities and Exchange Commission (“SEC”), the Fund may participate in a joint lending and borrowing facility for temporary purposes (the “Interfund Lending Program”), subject to compliance with the terms and conditions of the Order, and to the extent permitted by the Fund’s investment policies and restrictions. The Fund is currently permitted to borrow under the Interfund Lending Program.

A lending BlackRock fund may lend in aggregate up to 15% of its net assets, but may not lend more than 5% of its net assets to any one borrowing fund through the Interfund Lending Program. A borrowing BlackRock fund may not borrow through the Interfund Lending Program or from any other source more than 33 1/3% of its total assets (or any lower threshold provided for by the fund’s investment restrictions). If a borrowing BlackRock fund’s total outstanding borrowings exceed 10% of its total assets, each of its outstanding interfund loans will be subject to collateralization of at least 102% of the outstanding principal value of the loan. All interfund loans are for temporary or emergency purposes and the interest rate to be charged will be the average of the highest current overnight repurchase agreement rate available to a lending fund and the bank loan rate, as calculated according to a formula established by the Board.

22 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Notes to Financial Statements (unaudited) (continued)

During the six months ended March 31, 2021, the Fund did not participate in the Interfund Lending Program.

Directors and Officers: Certain directors and/or officers of the Corporation are directors and/or officers of BlackRock or its affiliates. The Fund reimburses the Manager for a portion of the compensation paid to the Corporation’s Chief Compliance Officer, which is included in Officer in the Statement of Operations.

5. INCOME TAX INFORMATION

It is the Fund’s policy to comply with the requirements of the Internal Revenue Code of 1986, as amended, applicable to regulated investment companies, and to distribute substantially all of its taxable income to its shareholders. Therefore, no U.S. federal income tax provision is required.

The Fund files U.S. federal and various state and local tax returns. No income tax returns are currently under examination. The statute of limitations on the Fund’s U.S. federal tax returns generally remains open for a period of three fiscal years after they are filed. The statutes of limitations on the Fund’s state and local tax returns may remain open for an additional year depending upon the jurisdiction.

Management has analyzed tax laws and regulations and their application to the Fund as of March 31, 2021, inclusive of the open tax return years, and does not believe that there are any uncertain tax positions that require recognition of a tax liability in the Fund’s financial statements.

6. CAPITAL SHARE TRANSACTIONS

Transactions in capital shares for each class were as follows:

	Six Months Ended 03/31/21						Year Ended 09/30/20
Share Class	Shares			Amounts			Shares			Amounts
Institutional
Shares sold		176,428,154		$	2,160,977,962			407,197,673		$	4,930,002,061
Shares issued in reinvestment of distributions		32,935,115			401,977,845			14,373,580			175,160,958
Shares redeemed		(130,448,423	)		(1,599,595,447	)		(244,952,396	)		(2,956,238,422	)
		78,914,846		$	963,360,360			176,618,857		$	2,148,924,597
Service
Shares sold		640,154		$	7,840,642			2,119,639		$	25,615,636
Shares issued in reinvestment of distributions		205,446			2,507,869			194,920			2,358,873
Shares redeemed		(879,615	)		(10,954,597	)		(7,758,975	)		(94,719,115	)
		(34,015	)	$	(606,086	)		(5,444,416	)	$	(66,744,606	)
Investor A
Shares sold and automatic conversion of shares		36,083,419		$	442,871,232			84,663,818		$	1,032,517,166
Shares issued in reinvestment of distributions		8,214,174			100,262,718			3,222,095			39,242,986
Shares redeemed		(27,687,299	)		(338,804,360	)		(70,592,751	)		(850,309,256	)
		16,610,294		$	204,329,590			17,293,162		$	221,450,896
Investor A1
Shares sold		144,465		$	1,779,483			522,733		$	6,411,563
Shares issued in reinvestment of distributions		80,809			985,665			37,182			451,698
Shares redeemed		(232,441	)		(2,839,099	)		(1,016,865	)		(12,228,873	)
		(7,167	)	$	(73,951	)		(456,950	)	$	(5,365,612	)
Investor C
Shares sold		1,038,558		$	12,826,571			3,772,518		$	45,891,628
Shares issued in reinvestment of distributions		451,749			5,510,193			217,692			2,637,204
Shares redeemed and automatic conversion of shares		(2,657,335	)		(32,667,286	)		(10,351,551	)		(128,116,264	)
		(1,167,028	)	$	(14,330,522	)		(6,361,341	)	$	(79,587,432	)
Investor C1(a)
Shares sold		—		$	—			8,015		$	95,808
Shares issued in reinvestment of distributions		—			—			1,289			15,443
Shares redeemed and automatic conversion of shares		—			—			(246,294	)		(2,992,951	)
		—		$	—			(236,990	)	$	(2,881,700	)

NOTES   TO   FINANCIAL   STATEMENTS 23

Notes to Financial Statements (unaudited) (continued)

	Six Months Ended 03/31/21						Year Ended 09/30/20
Share Class	Shares			Amounts			Shares			Amounts
Investor C2(a)
Shares sold		—		$	—			2,071		$	24,731
Shares issued in reinvestment of distributions		—			—			357			4,268
Shares redeemed and automatic conversion of shares		—			—			(60,923	)		(735,119	)
		—		$	—			(58,495	)	$	(706,120	)
Class K
Shares sold		134,994,136		$	1,644,446,657			202,032,912		$	2,461,899,430
Shares issued in reinvestment of distributions		27,195,595			331,892,487			13,179,979			160,520,192
Shares redeemed		(93,719,216	)		(1,159,340,346	)		(120,799,590	)		(1,450,443,307	)
		68,470,515		$	816,998,798			94,413,301		$	1,171,976,315
Class R
Shares sold		951,095		$	11,727,733			2,264,561		$	27,639,353
Shares issued in reinvestment of distributions		324,655			3,963,171			151,229			1,836,493
Shares redeemed		(1,065,702	)		(13,087,229	)		(7,529,338	)		(90,449,776	)
		210,048		$	2,603,675			(5,113,548	)	$	(60,973,930	)
		162,997,493		$	1,972,281,864			270,653,580		$	3,326,092,408

^(a)  On February 24, 2020, the Fund’s issued and outstanding Investor C1 and Investor C2 Shares converted into Investor A Shares.

7. SUBSEQUENT EVENTS

Management’s evaluation of the impact of all subsequent events on the Fund’s financial statements was completed through the date the financial statements were issued and the following item was noted:

Effective April 15, 2021, the credit agreement was extended until April 2022 under substantially the same terms.

24 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Portfolio Information as of March 31, 2021  Master Total Return Portfolio

PORTFOLIO COMPOSITION

Asset Type	Percent of    Total Investments(a)
U.S. Government Sponsored Agency Securities	44%
Corporate Bonds	28
Asset-Backed Securities	8
U.S. Treasury Obligations	7
Foreign Government Obligations	5
Non-Agency Mortgage-Backed Securities	4
Floating Rate Loan Interests	1
Common Stocks	1
Foreign Agency Obligations	1
Preferred Securities	1
Municipal Bonds	—(b)
Warrants	—(b)
Rights	—(b)

CREDIT QUALITY ALLOCATION

Credit Rating(c)	Percent of    Total Investments(a)
AAA/Aaa(d)	55%
AA/Aa	3
A	15
BBB/Baa	14
BB/Ba	4
B	2
CCC/Caa	1
N/R	6

^(a)  Total investments exclude short-term securities, options purchased, options written and TBA sale commitments.

^(b)  Amount is less than 1%.

^(c)  For financial reporting purposes, credit quality ratings shown above reflect the highest rating assigned by either S&P Global Ratings or Moody’s Investors Service (“Moody’s”) if ratings differ. These rating agencies are independent, nationally recognized statistical rating organizations and are widely used. Investment grade ratings are credit ratings of BBB/Baa or higher. Below investment grade ratings are credit ratings of BB/Ba or lower. Investments designated N/R are not rated by either rating agency. Unrated investments do not necessarily indicate low credit quality. Credit quality ratings are subject to change.

^(d)  The investment adviser evaluates the credit quality of unrated investments based upon certain factors including, but not limited to, credit ratings for similar investments and financial analysis of sectors, individual investments and/or issuers. Using this approach, the investment adviser has deemed unrated U.S. Government Sponsored Agency Securities and U.S. Treasury Obligations to be of similar credit quality as investments rated AAA/Aaa.

PORTFOLIO   INFORMATION 25

Schedule of Investments (unaudited) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities
510 Loan Acquisition Trust, Series 2020-1, Class A, 5.11%, 09/25/60(a)(b)(c)	USD		6,551	$	6,551,268
522 Funding CLO Ltd.
Series 2019-4A, Class CR, (3 mo. LIBOR US + 2.40%), 2.62%, 04/20/30(a)(d)			625		623,676
Series 2019-4A, Class DR, (3 mo. LIBOR US + 3.65%), 3.87%, 04/20/30(a)(d)			2,170		2,171,231
ACE Securities Corp. Home Equity Loan Trust
Series 2003-OP1, Class A2, (1 mo. LIBOR US + 0.72%), 0.83%, 12/25/33(d)			581		538,333
Series 2006-CW1, Class A2C, (1 mo. LIBOR US + 0.28%), 0.39%, 07/25/36(d)			334		298,403
Series 2007-HE4, Class A2A, (1 mo. LIBOR US + 0.26%), 0.37%, 05/25/37(d)			2,602		614,147
Series 2007-HE4, Class A2C, (1 mo. LIBOR US + 0.60%), 0.71%, 05/25/37(d)			230		57,084
Adams Mill CLO Ltd.
Series 2014-1A, Class A2R, (3 mo. LIBOR US + 1.10%), 1.34%, 07/15/26(a)(d)			2,080		2,080,344
Series 2014-1A, Class C1R, (3 mo. LIBOR US + 2.35%), 2.59%, 07/15/26(a)(d)			1,610		1,608,577
AGL CLO 6 Ltd., Series 2020-6A, Class E, (3 mo. LIBOR US + 7.48%), 7.70%, 07/20/31(a)(d)			375		375,517
AGL CLO 7 Ltd.
Series 2020-7A, Class A1, (3 mo. LIBOR US + 1.80%), 2.04%, 07/15/31(a)(d)			2,400		2,411,378
Series 2020-7A, Class D, (3 mo. LIBOR US + 4.40%), 4.64%, 07/15/31(a)(d)			500		502,047
AGL Core CLO 2 Ltd., Series 2019-2A, Class A1, (3 mo. LIBOR US + 1.39%), 1.61%, 04/20/32(a)(d)			8,405		8,438,209
AGL Core CLO 5 Ltd., Series 2020-5A, Class D, (3 mo. LIBOR US + 4.95%), 5.17%, 07/20/30(a)(b)(d)			1,750		1,758,400
AIMCO CLO
Series 2015-AA, Class BR, (3 mo. LIBOR US + 1.30%), 1.54%, 01/15/28(a)(d)			950		950,466
Series 2017-AA, Class A, (3 mo. LIBOR US + 1.26%), 1.48%, 07/20/29(a)(d)			500		501,255
Series 2017-AA, Class AR, (3 mo. LIBOR US + 1.05%), 0.00%, 04/20/34(a)(d)			250		250,000
Series 2017-AA, Class C, (3 mo. LIBOR US + 2.45%), 2.67%, 07/20/29(a)(d)			500		499,272
Series 2017-AA, Class CR, (3 mo. LIBOR US + 2.10%), 0.00%, 04/20/34(a)(d)			500		500,000
Series 2017-AA, Class DR, (3 mo. LIBOR US + 3.15%), 0.00%, 04/20/34(a)(d)			250		250,000
Ajax Mortgage Loan Trust
Series 2017-D, Class A, 3.75%, 12/25/57(a)			7,750		7,868,098
Series 2017-D, Class B, 0.00%, 12/25/57(a)(b)(d)			1,681		1,319,361
Series 2018-A, Class A, 3.85%, 04/25/58(a)(b)			8,190		8,210,917
Series 2018-A, Class B, 0.00%, 04/25/58(a)			2,641		1,447,156
Series 2018-B, Class A, 3.75%, 02/26/57(a)(b)			3,640		3,641,738
Series 2018-B, Class B, 0.00%, 02/26/57(a)			2,584		737,806
Series 2018-D, Class A, 3.75%, 08/25/58(a)(b)(d)			9,632		9,656,433
Series 2018-D, Class B, 0.00%, 08/25/58(a)(b)(d)			2,841		1,831,615

Security		Par (000)		Value
Asset-Backed Securities (continued)
Ajax Mortgage Loan Trust
Series 2018-E, Class A, 4.38%, 06/25/58(a)(d)	USD		4,237	$	4,278,085
Series 2018-E, Class B, 5.25%, 06/25/58(a)(b)(d)			840		845,712
Series 2018-E, Class C, 0.00%, 06/25/58(a)(b)(d)			2,104		1,577,677
Series 2018-F, Class A, 4.38%, 11/25/58(a)(b)(d)			13,288		13,452,722
Series 2018-F, Class B, 5.25%, 11/25/58(a)(b)(d)			2,415		2,432,296
Series 2018-F, Class C, 0.00%, 11/25/58(a)(b)			5,573		3,344,083
Series 2018-G, Class A, 4.38%, 06/25/57(a)(b)(d)			10,395		10,384,993
Series 2018-G, Class B, 5.25%, 06/25/57(a)(b)(d)			2,042		1,541,710
Series 2018-G, Class C, 0.00%, 06/25/57(a)(b)			5,261		5,173,482
Series 2019-A, Class A, 3.75%, 08/25/57(a)(d)			10,152		10,306,307
Series 2019-A, Class B, 5.25%, 08/25/57(a)(d)			1,720		1,702,845
Series 2019-A, Class C, 0.00%, 08/25/57(a)(b)			4,304		3,565,247
Series 2019-B, Class A, 3.75%, 01/25/59(a)(d)			17,523		17,789,950
Series 2019-B, Class B, 5.25%, 01/25/59(a)(b)(d)			2,845		2,147,975
Series 2019-B, Class C, 0.00%, 01/25/59(a)(b)			7,275		6,244,406
Series 2019-C, Class A, 3.95%, 10/25/58(a)(d)			5,947		5,955,835
Series 2019-E, Class A, 3.00%, 09/25/59(a)(c)			19,085		19,176,337
Series 2019-E, Class B, 4.88%, 09/25/59(a)(c)			2,600		2,553,968
Series 2019-E, Class C, 0.00%, 09/25/59(a)			5,767		3,857,209
Series 2019-G, Class A, 3.00%, 09/25/59(a)(c)			14,626		14,720,972
Series 2019-G, Class B, 4.25%, 09/25/59(a)(c)			2,120		2,054,857
Series 2019-G, Class C, 0.00%, 09/25/59(a)			5,419		4,545,991
Series 2019-H, Class A, 3.00%, 11/25/59(a)(c)			11,346		11,425,773
Series 2019-H, Class B, 4.25%, 11/25/59(a)(c)			1,970		1,909,466
Series 2019-H, Class C, 0.00%, 11/25/59(a)			4,879		4,327,948
Series 2020-A, Class A, 2.38%, 12/25/59(a)(c)			25,971		25,963,492
Series 2020-A, Class B, 3.50%, 12/25/59(a)(c)			3,853		3,844,166
Series 2020-A, Class C, 0.00%, 12/25/59(a)(b)			9,290		5,825,035
Series 2020-C, Class A, 2.25%, 09/27/60(a)(c)			29,003		28,960,910
Series 2020-C, Class B, 5.00%, 09/27/60(a)(c)			2,981		2,986,198
Series 2020-C, Class C, 0.00%, 09/27/60(a)			10,121		8,840,722
Series 2020-D, Class A, 2.25%, 06/25/60(a)(c)			27,929		27,888,648
Series 2020-D, Class B, 5.00%, 06/25/60(a)(c)			4,238		4,245,873

26 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Ajax Mortgage Loan Trust
Series 2020-D, Class C, 0.00%, 06/25/60(a)	USD		10,882	$	9,227,071
Allegro CLO II-S Ltd., Series 2014-1RA, Class A1, (3 mo. LIBOR US + 1.08%), 1.30%, 10/21/28(a)(d)			3,790		3,786,069
Allegro CLO IV Ltd.
Series 2016-1A, Class AR, (3 mo. LIBOR US + 1.15%), 1.39%, 01/15/30(a)(d)			6,568		6,567,994
Series 2016-1A, Class BR, (3 mo. LIBOR US + 1.70%), 1.94%, 01/15/30(a)(d)			2,530		2,537,199
ALM 2020 Ltd., Series 2020-1A, Class A2, (3 mo. LIBOR US + 1.85%), 2.09%, 10/15/29(a)(d)			7,780		7,776,044
ALM VII Ltd.
Series 2012-7A, Class A1A2, (3 mo. LIBOR US + 1.17%), 1.41%, 07/15/29(a)(d)			750		749,642
Series 2012-7A, Class A2R2, (3 mo. LIBOR US + 1.85%), 2.09%, 07/15/29(a)(d)			591		590,973
ALM VII R-2 Ltd., Series 2013-7R2A, Class CR2, (3 mo. LIBOR US + 3.00%), 3.24%, 10/15/27(a)(d)			500		496,890
ALM XIX Ltd.
Series 2016-19A, Class A1RA, (3 mo. LIBOR US + 1.00%), 1.24%, 04/16/29(a)(b)(d)			750		750,450
Series 2016-19A, Class A1RB, (3 mo. LIBOR US + 1.35%), 1.59%, 04/16/29(a)(b)(d)			500		500,000
Series 2016-19A, Class A2RA, (3 mo. LIBOR US + 1.45%), 1.69%, 04/16/29(a)(b)(d)			3,370		3,371,348
ALM XVIII Ltd., Series 2016-18A, Class A2R, (3 mo. LIBOR US + 1.65%), 1.89%, 01/15/28(a)(d)			1,250		1,247,881
ALME Loan Funding V BV, Series 5A, Class ER, (3 mo. EURIBOR + 5.41%), 5.41%, 07/15/31(a)(d)	EUR		1,500		1,724,216
AMMC CLO 21 Ltd., Series 2017-21A, Class A, (3 mo. LIBOR US + 1.25%), 1.45%, 11/02/30(a)(d)	USD		750		750,144
AMMC CLO 22 Ltd., Series 2018-22A, Class B, (3 mo. LIBOR US + 1.45%), 1.67%, 04/25/31(a)(d)			500		501,000
AMMC CLO XII Ltd., Series 2013-12A, Class AR, (3 mo. LIBOR US + 1.20%), 1.40%, 11/10/30(a)(d)			540		540,643
AMMC CLO XIII Ltd., Series 2013-13A, Class A1LR, (3 mo. LIBOR US + 1.26%), 1.48%, 07/24/29(a)(d)			2,592		2,590,265
AMSR Trust
Series 2020-SFR1, Class E, 3.22%, 04/17/37(a)			1,280		1,301,319
Series 2020-SFR2, Class D, 3.28%, 07/17/37(a)			2,437		2,511,746
Series 2020-SFR3, Class E 1, 2.56%, 09/17/37(a)			2,490		2,499,797
Series 2020-SFR4, Class E 2, 2.46%, 11/17/37(a)			2,500		2,479,718
Series 2020-SFR4, Class F, 2.86%, 11/17/37(a)			2,760		2,721,457
Anchorage Capital CLO 3-R Ltd.
Series 2014-3RA, Class A, (3 mo. LIBOR US + 1.05%), 1.27%, 01/28/31(a)(d)			2,120		2,120,514
Series 2014-3RA, Class B, (3 mo. LIBOR US + 1.50%), 1.72%, 01/28/31(a)(d)			3,600		3,595,792

Security		Par (000)		Value
Asset-Backed Securities (continued)
Anchorage Capital CLO 3-R Ltd.
Series 2014-3RA, Class C, (3 mo. LIBOR US + 1.85%), 2.07%, 01/28/31(a)(d)	USD		500	$	496,698
Anchorage Capital CLO 4-R Ltd.
Series 2014-4RA, Class A, (3 mo. LIBOR US + 1.05%), 1.27%, 01/28/31(a)(d)			5,330		5,331,269
Series 2014-4RA, Class C, (3 mo. LIBOR US + 1.85%), 2.07%, 01/28/31(a)(d)			5,550		5,518,787
Anchorage Capital CLO 5-R Ltd.
Series 2014-5RA, Class B, (3 mo. LIBOR US + 1.45%), 1.69%, 01/15/30(a)(d)			9,200		9,063,048
Series 2014-5RA, Class C, (3 mo. LIBOR US + 1.85%), 2.09%, 01/15/30(a)(d)			3,540		3,534,106
Anchorage Capital CLO 6 Ltd., Series 2015-6A, Class AR, (3 mo. LIBOR US + 1.27%), 1.51%, 07/15/30(a)(d)			4,010		4,010,727
Anchorage Capital CLO 7 Ltd.
Series 2015-7A, Class AR2, (3 mo. LIBOR US + 1.09%), 1.31%, 01/28/31(a)(d)			4,936		4,934,586
Series 2015-7A, Class BR2, (3 mo. LIBOR US + 1.75%), 1.97%, 01/28/31(a)(d)			7,620		7,611,351
Series 2015-7A, Class CR2, (3 mo. LIBOR US + 2.20%), 2.42%, 01/28/31(a)(d)			4,250		4,232,292
Series 2015-7A, Class D1R2, (3 mo. LIBOR US + 3.50%), 3.72%, 01/28/31(a)(d)			1,140		1,143,313
Anchorage Capital CLO 8 Ltd.
Series 2016-8A, Class AR, (3 mo. LIBOR US + 1.00%), 1.22%, 07/28/28(a)(d)			1,967		1,963,758
Series 2016-8A, Class BR, (3 mo. LIBOR US + 1.60%), 1.82%, 07/28/28(a)(d)			3,050		3,055,340
Anchorage Capital CLO Ltd.
Series 2013-1A, Class A1R, (3 mo. LIBOR US + 1.25%), 1.47%, 10/13/30(a)(d)			2,755		2,757,343
Series 2013-1A, Class A2R, (3 mo. LIBOR US + 1.65%), 1.88%, 10/13/30(a)(d)			750		749,167
Series 2013-1A, Class BR, (3 mo. LIBOR US + 2.15%), 2.37%, 10/13/30(a)(d)			1,410		1,408,023
Anchorage Capital Europe CLO 2 DAC
Series 2A, Class B, (3 mo. EURIBOR + 1.80%), 1.80%, 05/15/31(a)(d)	EUR		250		292,087
Series 2A, Class B1R, (3 mo. EURIBOR + 1.60%), 0.00%, 04/15/34(a)(d)			2,421		2,839,107
Series 2A, Class CR, (3 mo. EURIBOR + 2.40%), 0.00%, 04/15/34(a)(d)			1,298		1,522,165
Series 2A, Class DR, (3 mo. EURIBOR + 3.55%), 0.00%, 04/15/34(a)(d)			2,130		2,497,851
Series 2A, Class ER, (3 mo. EURIBOR + 6.45%), 0.00%, 04/15/34(a)(d)			460		528,653
Anchorage Capital Europe CLO DAC, Series 4A, Class D, (3 mo. EURIBOR + 3.20%), 3.20%, 04/25/34(a)(d)			1,042		1,211,897
Apidos CLO XII, Series 2013-12A, Class AR, (3 mo. LIBOR US + 1.08%), 1.32%, 04/15/31(a)(d)	USD		3,152		3,153,712
Apidos CLO XV, Series 2013-15A, Class A1RR, (3 mo. LIBOR US + 1.01%), 1.23%, 04/20/31(a)(d)			1,080		1,075,738
Apidos CLO XVIII, Series 2018-18A, Class A1, (3 mo. LIBOR US + 1.14%), 1.36%, 10/22/30(a)(d)			880		879,055

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 27

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Apidos CLO XX, Series 2015-20A, Class A2RR, (3 mo. LIBOR US + 1.55%), 1.77%, 07/16/31(a)(d)	USD		250	$	247,019
Apidos CLO XXII
Series 2015-22A, Class A2R, (3 mo. LIBOR US + 1.50%), 1.72%, 04/20/31(a)(d)			500		501,070
Series 2015-22A, Class CR, (3 mo. LIBOR US + 2.95%), 3.17%, 04/20/31(a)(d)			850		844,578
Apidos CLO XXXI, Series 2019-31A, Class B, (3 mo. LIBOR US + 1.90%), 2.14%, 04/15/31(a)(d)			2,950		2,945,558
Apres Static CLO Ltd., Series 2019-1A, Class A2R, (3 mo. LIBOR US + 1.70%), 1.94%, 10/15/28(a)(d)			250		250,392
Aqueduct European CLO DAC
Series 2019-4A, Class B1, (3 mo. EURIBOR + 1.80%), 1.80%, 07/15/32(a)(d)	EUR		750		876,987
Series 2019-4X, Class B1, (3 mo. EURIBOR + 1.80%), 1.80%, 07/15/32(d)			1,560		1,824,132
Arbour CLO II DAC, Series 2014-2X, Class B2R, (3 mo. EURIBOR + 1.50%), 1.50%, 05/15/30(d)			995		1,165,542
Arbour CLO VIII DAC, Series 8A, Class C, (3 mo. EURIBOR + 2.90%), 2.90%, 07/15/33(a)(b)(d)			550		649,493
Ares European CLO X BV, Series 10X, Class B1, (3 mo. EURIBOR + 1.70%), 1.70%, 10/15/31(d)			820		960,722
Ares European CLO XI BV, Series 11X, Class B1, (3 mo. EURIBOR + 1.85%), 1.85%, 04/15/32(d)			730		853,284
Ares European CLO XII BV, Series 12X, Class B1, (3 mo. EURIBOR + 1.75%), 1.75%, 04/20/32(d)			1,370		1,609,987
Ares LIX CLO Ltd., Series 2021-59A, Class E, (3 mo. LIBOR US + 6.25%), 0.00%, 04/25/34(a)(d)	USD		250		250,000
Ares LVI CLO Ltd., Series 2020-56A, Class E, (3 mo. LIBOR US + 7.58%), 7.79%, 10/25/31(a)(d)			1,720		1,729,196
Ares LVIII CLO Ltd., Series 2020-58A, Class E, (3 mo. LIBOR US + 7.03%), 7.27%, 01/15/33(a)(d)			250		250,742
Ares XXXVII CLO Ltd., Series 2015-4A, Class A1R, (3 mo. LIBOR US + 1.17%), 1.41%, 10/15/30(a)(d)			1,150		1,151,299
Argent Mortgage Loan Trust, Series 2005-W1, Class A2, (1 mo. LIBOR US + 0.24%), 0.59%, 05/25/35(d)			3,548		3,260,981
Armada Euro CLO III DAC
Series 3A, Class CR, (3 mo. EURIBOR + 2.35%), 0.00%, 07/15/31(a)(b)(d)	EUR		2,880		3,377,376
Series 3A, Class DR, (3 mo. EURIBOR + 3.30%), 0.00%, 07/15/31(a)(b)(d)			1,313		1,539,755
Assurant CLO I Ltd.
Series 2017-1A, Class B, (3 mo. LIBOR US + 1.70%), 1.92%, 10/20/29(a)(d)	USD		1,400		1,396,517
Series 2017-1A, Class C, (3 mo. LIBOR US + 2.10%), 2.32%, 10/20/29(a)(d)			1,420		1,417,705
Atrium IX, Series 9A, Class AR2, (3 mo. LIBOR US + 0.99%), 1.18%, 05/28/30(a)(b)(d)			4,010		4,010,401

Security		Par (000)		Value
Asset-Backed Securities (continued)
Atrium XII
Series 12A, Class AR, (3 mo. LIBOR US + 0.83%), 1.05%, 04/22/27(a)(d)	USD		1,538	$	1,538,214
Series 12A, Class CR, (3 mo. LIBOR US + 1.65%), 1.87%, 04/22/27(a)(d)			2,381		2,356,005
Atrium XIII, Series 13A, Class B, (3 mo. LIBOR US + 1.50%), 1.72%, 11/21/30(a)(d)			1,000		993,234
Avery Point IV CLO Ltd., Series 2014-1A, Class AR, (3 mo. LIBOR US + 1.10%), 1.32%, 04/25/26(a)(d)			383		383,390
Avery Point V CLO Ltd.
Series 2014-5A, Class AR, (3 mo. LIBOR US + 0.98%), 1.20%, 07/17/26(a)(d)			667		667,198
Series 2014-5A, Class BR, (3 mo. LIBOR US + 1.50%), 1.72%, 07/17/26(a)(d)			2,250		2,243,843
Avery Point VI CLO Ltd.
Series 2015-6A, Class AR2, (3 mo. LIBOR US + 0.90%), 1.06%, 08/05/27(a)(d)			4,665		4,660,443
Series 2015-6A, Class BR2, (3 mo. LIBOR US + 1.35%), 1.51%, 08/05/27(a)(d)			3,900		3,895,870
Avery Point VII CLO Ltd., Series 2015-7A, Class AR2, (3 mo. LIBOR US + 0.96%), 1.20%, 01/15/28(a)(d)			7,480		7,470,881
Avoca CLO XII Ltd., Series 12X, Class CR, (3 mo. EURIBOR + 2.05%), 2.05%, 04/15/30(d)	EUR		475		555,432
Avoca CLO XV DAC, Series 15X, Class B2R, (3 mo. EURIBOR + 1.05%), 1.05%, 04/15/31(d)			400		462,652
Avoca CLO XVII DAC, Series 17A, Class B1R, (3 mo. EURIBOR + 1.70%), 1.70%, 10/15/32(a)(d)			1,390		1,623,612
Avoca CLO XVIII DAC, Series 18X, Class C, (3 mo. EURIBOR + 1.75%), 1.75%, 04/15/31(d)			400		463,513
Avoca CLO XX DAC, Series 20X, Class E, (3 mo. EURIBOR + 5.75%), 5.75%, 07/15/32(d)			1,040		1,187,756
Avoca CLO XXII DAC, Series 22A, Class D, (3 mo. EURIBOR + 2.90%), 2.90%, 04/15/35(a)(b)(d)			500		586,350
Babson CLO Ltd.
Series 2015-2A, Class AR, (3 mo. LIBOR US + 1.19%), 1.41%, 10/20/30(a)(d)	USD		2,590		2,588,110
Series 2015-IA, Class BR, (3 mo. LIBOR US + 1.40%), 1.62%, 01/20/31(a)(d)			610		611,528
Bain Capital Credit CLO Ltd.
Series 2016-2A, Class ARR, (3 mo. LIBOR US + 0.97%), 0.00%, 01/15/29(a)(d)			1,350		1,348,199
Series 2016-2A, Class BRR, (3 mo. LIBOR US + 1.55%), 0.00%, 01/15/29(a)(d)			1,000		996,057
Series 2018-2A, Class A1, (3 mo. LIBOR US + 1.08%), 1.30%, 07/19/31(a)(d)			1,420		1,416,363
Series 2018-2A, Class B, (3 mo. LIBOR US + 1.60%), 1.82%, 07/19/31(a)(d)			500		500,451
Series 2019-1A, Class C, (3 mo. LIBOR US + 2.75%), 2.97%, 04/18/32(a)(d)			500		498,447
Series 2019-3A, Class C, (3 mo. LIBOR US + 2.85%), 3.07%, 10/21/32(a)(d)			500		499,985
Bain Capital Euro CLO DAC, Series 2019-1X,
Class C, (3 mo. EURIBOR + 2.40%), 2.40%, 04/15/32(d)	EUR		1,160		1,354,854

28 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Ballyrock CLO Ltd.
Series 2016-1A, Class DR2, (3 mo. LIBOR US + 3.15%), 3.39%, 10/15/28(a)(d)	USD		500	$	496,301
Series 2020-1A, Class C, (3 mo. LIBOR US + 4.50%), 4.72%, 07/20/30(a)(d)			400		401,850
BankAmerica Manufactured Housing Contract Trust
Series 1997-2, Class B1, 7.07%, 02/10/22(d)			1,680		867,388
Series 1998-2, Class B1, 7.43%, 12/10/25(d)			2,790		1,178,170
Barings CLO Ltd., Series 2018-3A, Class A1, (3 mo. LIBOR US + 0.95%), 1.17%, 07/20/29(a)(d)			1,085		1,085,000
Battalion CLO 18 Ltd.
Series 2020-18A, Class B, (3 mo. LIBOR US + 2.30%), 2.54%, 10/15/32(a)(d)			1,827		1,829,941
Series 2020-18A, Class D1, (3 mo. LIBOR US + 4.00%), 4.24%, 10/15/32(a)(d)			1,617		1,620,128
Battalion CLO VII Ltd., Series 2014-7A, Class A1RR, (3 mo. LIBOR US + 1.04%), 1.26%, 07/17/28(a)(d)			2,717		2,717,945
Battalion CLO VIII Ltd.
Series 2015-8A, Class A1R2, (3 mo. LIBOR US + 1.07%), 1.29%, 07/18/30(a)(d)			6,500		6,499,989
Series 2015-8A, Class A2R2, (3 mo. LIBOR US + 1.55%), 1.77%, 07/18/30(a)(d)			3,250		3,202,471
Series 2015-8A, Class BR2, (3 mo. LIBOR US + 2.00%), 2.22%, 07/18/30(a)(d)			2,901		2,896,609
Battalion CLO X Ltd.
Series 2016-10A, Class A1R2, (3 mo. LIBOR US + 1.17%), 1.29%, 01/25/35(a)(d)			25,430		25,322,312
Series 2016-10A, Class A2R2, (3 mo. LIBOR US + 1.55%), 1.67%, 01/25/35(a)(d)			2,890		2,883,213
Bayview Financial Revolving Asset Trust
Series 2004-B, Class A1, (1 mo. LIBOR US + 1.00%), 1.11%, 05/28/39(a)(d)			9,690		9,082,645
Series 2004-B, Class A2, (1 mo. LIBOR US + 1.30%), 1.41%, 05/28/39(a)(d)			461		389,446
Series 2005-A, Class A1, (1 mo. LIBOR US + 1.00%), 1.11%, 02/28/40(a)(d)			2,142		2,044,437
Series 2005-E, Class A1, (1 mo. LIBOR US + 1.00%), 1.11%, 12/28/40(a)(d)			742		668,097
BCMSC Trust
Series 2000-A, Class A2, 7.58%, 06/15/30(d)			1,674		419,729
Series 2000-A, Class A3, 7.83%, 06/15/30(d)			1,554		402,676
Series 2000-A, Class A4, 8.29%, 06/15/30(d)			1,121		307,540
BDS Ltd., Series 2019-FL3, Class A, (1 mo. LIBOR US + 1.40%), 1.51%, 12/15/35(a)(d)			3,997		3,997,649
Bear Stearns Asset-Backed Securities I Trust
Series 2004-HE7, Class M2, (1 mo. LIBOR US + 1.73%), 1.83%, 08/25/34(d)			149		149,318
Series 2006-HE1, Class 1M4, (1 mo. LIBOR US + 1.02%), 1.13%, 12/25/35(d)			1,689		2,318,904
Series 2006-HE7, Class 1A2, (1 mo. LIBOR US + 0.17%), 0.28%, 09/25/36(d)			2,079		2,008,458
Series 2007-FS1, Class 1A3, (1 mo. LIBOR US + 0.17%), 0.28%, 05/25/35(d)			536		523,265
Series 2007-HE1, Class 21A2, (1 mo. LIBOR US + 0.16%), 0.27%, 01/25/37(d)			502		490,924
Series 2007-HE2, Class 1A4, (1 mo. LIBOR US + 0.32%), 0.43%, 03/25/37(d)			1,153		1,036,708
Series 2007-HE2, Class 22A, (1 mo. LIBOR US + 0.14%), 0.25%, 03/25/37(d)			668		638,857

Security		Par (000)		Value
Asset-Backed Securities (continued)
Bear Stearns Asset-Backed Securities I Trust
Series 2007-HE2, Class 23A, (1 mo. LIBOR US + 0.14%), 0.25%, 03/25/37(d)	USD		1,366	$	1,290,915
Series 2007-HE3, Class 1A3, (1 mo. LIBOR US + 0.25%), 0.36%, 04/25/37(d)			908		1,052,690
Series 2007-HE3, Class 1A4, (1 mo. LIBOR US + 0.35%), 0.46%, 04/25/37(d)			6,111		5,894,874
Beechwood Park CLO Ltd., Series 2019-1A, Class B2A, (3 mo. LIBOR US + 1.75%), 1.97%, 01/17/33(a)(d)			1,500		1,504,200
Benefit Street Partners CLO II Ltd., Series 2013-IIA, Class A2R2, (3 mo. LIBOR US + 1.45%), 1.69%, 07/15/29(a)(d)			3,160		3,156,359
Benefit Street Partners CLO III Ltd., Series 2013-IIIA, Class A1R, (3 mo. LIBOR US + 1.25%), 1.47%, 07/20/29(a)(d)			749		749,286
Benefit Street Partners CLO Ltd., Series 2021- 23A, Class E, (3 mo. LIBOR US + 6.81%), 0.00%, 04/25/34(a)(d)			750		735,000
Benefit Street Partners CLO V-B Ltd., Series 2018-5BA, Class A1A, (3 mo. LIBOR US + 1.09%), 1.31%, 04/20/31(a)(d)			4,360		4,355,596
Benefit Street Partners CLO VI Ltd.
Series 2015-VIA, Class A1R, (3 mo. LIBOR US + 1.24%), 1.46%, 10/18/29(a)(d)			12,030		12,032,484
Series 2015-VIA, Class A2R, (3 mo. LIBOR US + 1.72%), 1.94%, 10/18/29(a)(d)			3,320		3,326,763
Benefit Street Partners CLO VII Ltd.
Series 2015-VIIA, Class A1AR, (3 mo. LIBOR US + 0.78%), 1.00%, 07/18/27(a)(d)			939		938,911
Series 2015-VIIA, Class CR, (3 mo. LIBOR US + 2.40%), 2.62%, 07/18/27(a)(d)			600		595,183
Benefit Street Partners CLO VIII Ltd., Series 2015-8A, Class A1AR, (3 mo. LIBOR US + 1.10%), 1.32%, 01/20/31(a)(d)			1,250		1,251,405
Benefit Street Partners CLO XX Ltd., Series 2020-20A, Class D, (3 mo. LIBOR US + 4.25%), 4.49%, 07/15/31(a)(d)			3,010		3,020,991
Benefit Street Partners CLO XXI Ltd., Series 2020-21A, Class E, (3 mo. LIBOR US + 8.04%), 8.28%, 07/15/31(a)(d)			250		250,707
Birch Grove CLO Ltd.
Series 19A, Class C, (3 mo. LIBOR US + 2.95%), 3.13%, 06/15/31(a)(d)			1,250		1,247,553
Series 19A, Class D, (3 mo. LIBOR US + 3.90%), 4.08%, 06/15/31(a)(d)			1,195		1,195,621
BlueMountain CLO Ltd.
Series 2012-2A, Class AR2, (3 mo. LIBOR US + 1.05%), 1.23%, 11/20/28(a)(d)			1,454		1,453,995
Series 2013-1A, Class A1R2, (3 mo. LIBOR US + 1.23%), 1.45%, 01/20/29(a)(d)			3,638		3,640,434
Series 2013-2A, Class A1R, (3 mo. LIBOR US + 1.18%), 1.40%, 10/22/30(a)(d)			6,245		6,247,535
Series 2015-3A, Class A1R, (3 mo. LIBOR US + 1.00%), 1.22%, 04/20/31(a)(d)			2,550		2,542,856
BlueMountain CLO XXII Ltd., Series 2018-22A, Class B, (3 mo. LIBOR US + 1.50%), 1.74%, 07/15/31(a)(d)			3,970		3,944,598
BlueMountain CLO XXIV Ltd., Series 2019-24A, Class C, (3 mo. LIBOR US + 2.70%), 2.92%, 04/20/31(a)(d)			1,200		1,196,436

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 29

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
BlueMountain CLO XXIX Ltd., Series 2020-29A, Class B, (3 mo. LIBOR US + 2.25%), 2.47%, 07/25/31(a)(d)	USD		750	$	753,624
BlueMountain CLO XXV Ltd., Series 2019-25A, Class E, (3 mo. LIBOR US + 6.70%), 6.94%, 07/15/32(a)(d)			1,000		1,002,581
BlueMountain EUR CLO DAC, Series 2021-1A, Class D, (3 mo. EURIBOR + 3.20%), 3.20%, 04/15/34(a)(b)(d)	EUR		1,500		1,754,652
BlueMountain Fuji Eur CLO IV DAC, Series 4X, Class A2, (3 mo. EURIBOR + 1.35%), 1.35%, 03/30/32(d)			670		785,203
BlueMountain Fuji Eur CLO V DAC, Series 5X, Class C, (3 mo. EURIBOR + 2.45%), 2.45%, 01/15/33(d)			1,560		1,825,244
Brex Commercial Charge Card Master Trust, Series 2021-1, Class A, 2.09%, 07/17/24(a)	USD		5,290		5,294,959
Brookside Mill CLO Ltd.
Series 2013-1A, Class BR, (3 mo. LIBOR US + 1.35%), 1.57%, 01/17/28(a)(d)			500		500,447
Series 2013-1A, Class DR, (3 mo. LIBOR US + 2.65%), 2.87%, 01/17/28(a)(d)			1,073		1,035,690
Buttermilk Park CLO Ltd., Series 2018-1A, Class D, (3 mo. LIBOR US + 3.10%), 3.34%, 10/15/31(a)(d)			625		625,072
Cairn CLO XII DAC
Series 2020-12A, Class B, (3 mo. EURIBOR + 2.30%), 2.30%, 04/15/33(a)(b)(d)	EUR		500		592,917
Series 2020-12A, Class C, (3 mo. EURIBOR + 3.00%), 3.00%, 04/15/33(a)(b)(d)			1,175		1,394,871
Canyon CLO Ltd., Series 2020-3A, Class B, (3 mo. LIBOR US + 1.70%), 1.93%, 01/15/34(a)(d)	USD		1,610		1,606,224
Carlyle C17 CLO Ltd., Series C17A, Class A1AR, (3 mo. LIBOR US + 1.03%), 1.24%, 04/30/31(a)(d)			7,620		7,613,645
Carlyle Global Market Strategies CLO Ltd.
Series 2013-2A, Class AR, (3 mo. LIBOR US + 0.89%), 1.11%, 01/18/29(a)(d)			1,488		1,484,643
Series 2013-3A, Class A1AR, (3 mo. LIBOR US + 1.10%), 1.34%, 10/15/30(a)(d)			248		248,550
Series 2013-4A, Class A1RR, (3 mo. LIBOR US + 1.00%), 1.24%, 01/15/31(a)(d)			1,853		1,849,669
Series 2014-1A, Class A1R2, (3 mo. LIBOR US + 0.97%), 1.19%, 04/17/31(a)(d)			3,160		3,157,257
Series 2015-3A, Class A2R, (3 mo. LIBOR US + 1.60%), 1.82%, 07/28/28(a)(d)			2,470		2,472,116
Carlyle U.S. CLO Ltd.
Series 2016-4A, Class A2R, (3 mo. LIBOR US + 1.45%), 1.67%, 10/20/27(a)(d)			750		747,680
Series 2017-4A, Class A1, (3 mo. LIBOR US + 1.18%), 1.42%, 01/15/30(a)(d)			4,620		4,621,610
Series 2018-1A, Class A2, (3 mo. LIBOR US + 1.50%), 1.72%, 04/20/31(a)(d)			250		247,916
Series 2019-2A, Class A1, (3 mo. LIBOR US + 1.28%), 1.52%, 07/15/32(a)(d)			4,000		4,004,857
Series 2020-1A, Class C1, (3 mo. LIBOR US + 4.00%), 4.22%, 07/20/31(a)(d)			750		752,320
Carrington Mortgage Loan Trust
Series 2006-NC1, Class M2, (1 mo. LIBOR US + 0.42%), 0.53%, 01/25/36(d)			610		534,840

Security		Par (000)		Value
Asset-Backed Securities (continued)
Carrington Mortgage Loan Trust
Series 2006-NC3, Class A3, (1 mo. LIBOR US + 0.15%), 0.26%, 08/25/36(d)	USD		3,208	$	3,074,277
Series 2006-NC4, Class A3, (1 mo. LIBOR US + 0.16%), 0.27%, 10/25/36(d)			682		659,097
Series 2006-NC5, Class A3, (1 mo. LIBOR US + 0.15%), 0.26%, 01/25/37(d)			3,978		3,565,064
CarVal CLO II Ltd.
Series 2019-1A, Class CR, (3 mo. LIBOR US + 2.00%), 0.00%, 04/20/32(a)(d)			700		696,732
Series 2019-1A, Class DR, (3 mo. LIBOR US + 3.20%), 0.00%, 04/20/32(a)(b)(d)			5,250		5,250,000
CarVal CLO III Ltd., Series 2019-2A, Class D, (3 mo. LIBOR US + 3.70%), 3.92%, 07/20/32(a)(d)			2,000		2,004,340
CarVal CLO Ltd., Series 2018-1A, Class D, (3 mo. LIBOR US + 2.89%), 3.11%, 07/16/31(a)(d)			500		497,070
Cascade MH Asset Trust, Series 2019-MH1, Class A, 4.00%, 11/25/44(a)(d)			10,906		11,421,809
CBAM Ltd.
Series 2017-1A, Class A1, (3 mo. LIBOR US + 1.25%), 1.47%, 07/20/30(a)(d)			6,050		6,050,005
Series 2017-2A, Class B1, (3 mo. LIBOR US + 1.75%), 1.97%, 10/17/29(a)(d)			2,955		2,955,810
Series 2017-3A, Class A, (3 mo. LIBOR US + 1.23%), 1.45%, 10/17/29(a)(d)			3,780		3,781,207
Series 2017-3A, Class B1, (3 mo. LIBOR US + 1.70%), 1.92%, 10/17/29(a)(d)			1,000		999,974
C-BASS Trust, Series 2006-CB7, Class A4, (1 mo. LIBOR US + 0.16%), 0.27%, 10/25/36(d)			552		466,899
CDO Repack SPC Ltd., Series 2006-CLF1, Class D1, 0.00%, 05/20/30(a)			287		294,523
Cedar Funding II CLO Ltd.
Series 2013-1A, Class A1R, (3 mo. LIBOR US + 1.23%), 1.42%, 06/09/30(a)(d)			1,511		1,511,930
Series 2013-1A, Class ARR, (3 mo. LIBOR US + 1.08%), 0.00%, 04/20/34(a)(d)			2,180		2,180,000
Series 2013-1A, Class BR, (3 mo. LIBOR US + 1.75%), 1.94%, 06/09/30(a)(d)			2,450		2,447,330
Series 2013-1A, Class BRR, (3 mo. LIBOR US + 1.35%), 0.00%, 04/20/34(a)(d)			3,110		3,110,000
Cedar Funding IV CLO Ltd.
Series 2014-4A, Class AR, (3 mo. LIBOR US + 1.23%), 1.45%, 07/23/30(a)(d)			3,790		3,791,292
Series 2014-4A, Class BR, (3 mo. LIBOR US + 1.60%), 1.82%, 07/23/30(a)(d)			750		749,712
Cedar Funding IX CLO Ltd., Series 2018-9A, Class A1, (3 mo. LIBOR US + 0.98%), 1.20%, 04/20/31(a)(d)			940		934,347
Cedar Funding V CLO Ltd., Series 2016-5A, Class A1R, (3 mo. LIBOR US + 1.10%), 1.32%, 07/17/31(a)(d)			2,130		2,132,068
Cedar Funding VI CLO Ltd.
Series 2016-6A, Class AR, (3 mo. LIBOR US + 1.09%), 1.31%, 10/20/28(a)(d)			15,035		15,048,103
Series 2016-6A, Class ARR, (3 mo. LIBOR US + 1.05%), 1.24%, 04/20/34(a)(d)			18,290		18,290,000
Series 2016-6A, Class CR, (3 mo. LIBOR US + 2.10%), 2.32%, 10/20/28(a)(d)			2,900		2,894,865

30 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Cedar Funding VIII CLO Ltd.
Series 2017-8A, Class A1, (3 mo. LIBOR US + 1.25%), 1.47%, 10/17/30(a)(d)	USD		16,520	$	16,526,397
Series 2017-8A, Class B, (3 mo. LIBOR US + 1.70%), 1.92%, 10/17/30(a)(d)			2,627		2,630,338
Series 2017-8A, Class C, (3 mo. LIBOR US + 2.25%), 2.47%, 10/17/30(a)(d)			750		748,558
CIFC European Funding CLO II DAC,
Series 2X, Class B1, (3 mo. EURIBOR + 1.60%), 1.60%, 04/15/33(d)	EUR		900		1,040,515
CIFC Funding Ltd.
Series 2012-2RA, Class A2, (3 mo. LIBOR US + 1.25%), 1.47%, 01/20/28(a)(d)	USD		750		747,686
Series 2013-1A, Class A2R, (3 mo. LIBOR US + 1.75%), 1.97%, 07/16/30(a)(d)			500		500,127
Series 2013-4A, Class BRR, (3 mo. LIBOR US + 1.60%), 1.81%, 04/27/31(a)(d)			500		498,460
Series 2014-2RA, Class B1, (3 mo. LIBOR US + 2.80%), 3.02%, 04/24/30(a)(d)			650		642,700
Series 2014-3A, Class BR2, (3 mo. LIBOR US + 1.80%), 2.02%, 10/22/31(a)(d)			700		698,800
Series 2014-4RA, Class A1A, (3 mo. LIBOR US + 1.13%), 1.35%, 10/17/30(a)(d)			26,820		26,822,001
Series 2014-4RA, Class A2, (3 mo. LIBOR US + 1.65%), 1.87%, 10/17/30(a)(d)			250		249,199
Series 2015-2A, Class AR2, (3 mo. LIBOR US + 1.01%), 1.25%, 04/15/30(a)(b)(d)			1,270		1,270,508
Series 2015-2A, Class CR2, (3 mo. LIBOR US + 2.00%), 2.24%, 04/15/30(a)(d)			2,904		2,881,514
Series 2015-3A, Class BR, 1.37%, 04/19/29(a)(d)			1,420		1,397,493
Series 2017-1A, Class AR, (3 mo. LIBOR US + 1.01%), 1.23%, 04/23/29(a)(d)			5,840		5,836,988
Series 2017-1A, Class B, (3 mo. LIBOR US + 1.70%), 1.92%, 04/23/29(a)(d)			2,910		2,907,098
Series 2017-5A, Class C, (3 mo. LIBOR US + 2.85%), 3.07%, 11/16/30(a)(d)			300		296,575
Series 2018-1A, Class A, (3 mo. LIBOR US + 1.00%), 1.22%, 04/18/31(a)(d)			1,834		1,831,456
Series 2019-4A, Class A2, (3 mo. LIBOR US + 1.80%), 2.04%, 07/15/32(a)(d)			400		400,325
Series 2019-5A, Class C, (3 mo. LIBOR US + 3.80%), 4.04%, 10/15/32(a)(d)			250		251,408
Series 2020-1A, Class B, (3 mo. LIBOR US + 2.30%), 2.54%, 07/15/32(a)(d)			3,260		3,262,581
Series 2020-1A, Class D, (3 mo. LIBOR US + 4.00%), 4.24%, 07/15/32(a)(d)			1,120		1,123,729
Citigroup Mortgage Loan Trust
Series 2007-AHL2, Class A3B, (1 mo. LIBOR US + 0.20%), 0.31%, 05/25/37(d)			5,996		4,802,795
Series 2007-AHL2, Class A3C, (1 mo. LIBOR US + 0.27%), 0.38%, 05/25/37(d)			2,724		2,198,958
Series 2007-AHL3, Class A3B, (1 mo. LIBOR US + 0.17%), 0.28%, 07/25/45(d)			4,467		3,849,870
Clear Creek CLO, Series 2015-1A, Class DR, (3 mo. LIBOR US + 2.95%), 3.17%, 10/20/30(a)(d)			620		607,784
Cloud Pass-Through Trust, Series 2019-1A, Class CLOU, 3.55%, 12/05/22(a)(d)			5,765		5,820,485
Conseco Finance Corp.
Series 1997-3, Class M1, 7.53%, 03/15/28(d)			1,208		1,222,205
Series 1997-6, Class M1, 7.21%, 01/15/29(d)			221		225,691

Security		Par (000)		Value
Asset-Backed Securities (continued)
Conseco Finance Corp.
Series 1998-4, Class M1, 6.83%, 04/01/30(d)	USD		339	$	329,974
Series 1998-8, Class A1, 6.28%, 09/01/30			469		490,934
Series 1998-8, Class M1, 6.98%, 09/01/30(d)			2,429		2,282,390
Series 1999-5, Class A5, 7.86%, 03/01/30(d)			920		540,346
Series 1999-5, Class A6, 7.50%, 03/01/30(d)			986		557,274
Series 2001-D, Class B1, (1 mo. LIBOR US + 2.50%), 2.61%, 11/15/32(d)			1,397		1,306,348
Conseco Finance Securitizations Corp.
Series 2000-1, Class A5, 8.06%, 09/01/29(d)			1,602		515,456
Series 2000-4, Class A6, 8.31%, 05/01/32(d)			1,373		431,906
Series 2000-5, Class A6, 7.96%, 05/01/31			2,194		1,032,218
Series 2000-5, Class A7, 8.20%, 05/01/31			4,002		1,939,461
Contego CLO VI DAC, Series 6A, Class CR, (3 mo. EURIBOR + 2.40%), 0.00%, 04/15/34(a)(d)	EUR		905		1,061,294
Contego CLO VIII DAC
Series 8A, Class B1, (3 mo. EURIBOR + 2.10%), 2.10%, 01/25/32(a)(d)			2,400		2,802,455
Series 8A, Class C, (3 mo. EURIBOR + 2.80%), 2.80%, 01/25/32(a)(b)(d)			500		593,093
Countrywide Asset-Backed Certificates
Series 2004-5, Class A, (1 mo. LIBOR US + 0.90%), 1.01%, 10/25/34(d)	USD		471		463,467
Series 2005-16, Class 1AF, 4.60%, 04/25/36(d)			3,148		3,078,189
Series 2005-17, Class 1AF4, 6.05%, 05/25/36(c)			1,673		1,639,661
Series 2006-1, Class AF4, 4.55%, 07/25/36(d)			1,314		1,328,907
Series 2006-11, Class 3AV2, (1 mo. LIBOR US + 0.16%), 0.27%, 09/25/46(d)			148		145,371
Series 2006-12, Class 1A, (1 mo. LIBOR US + 0.26%), 0.37%, 12/25/36(d)			2,106		2,028,624
Series 2006-17, Class 2A2, (1 mo. LIBOR US + 0.15%), 0.26%, 03/25/47(d)			183		179,730
Series 2006-18, Class M1, (1 mo. LIBOR US + 0.30%), 0.41%, 03/25/37(d)			6,211		5,802,961
Series 2006-8, Class 2A3, (1 mo. LIBOR US + 0.16%), 0.27%, 12/25/35(d)			319		317,267
Series 2006-8, Class 2A4, (1 mo. LIBOR US + 0.25%), 0.36%, 01/25/46(d)			8,384		8,061,794
Series 2006-S10, Class A3, (1 mo. LIBOR US + 0.32%), 0.43%, 10/25/36(d)			3,070		2,935,839
Series 2006-S3, Class A4, 6.44%, 01/25/29(c)			200		246,161
Series 2006-SPS1, Class A, (1 mo. LIBOR US + 0.22%), 0.33%, 12/25/25(d)			62		91,063
Series 2007-12, Class 1A2, (1 mo. LIBOR US + 0.84%), 0.95%, 08/25/47(d)			5,257		5,214,315
Countrywide Asset-Backed Certificates
Revolving Home Equity Loan Trust, Series 2004-U, Class 2A, (1 mo. LIBOR US + 0.27%), 0.38%, 03/15/34(d)			598		573,526
Credit Suisse First Boston Mortgage Securities Corp., Series 2001-MH29, Class B1, 8.10%, 09/25/31(d)			1,682		1,744,596
Credit-Based Asset Servicing & Securitization LLC
Series 2006-CB2, Class AF4, 3.10%, 12/25/36(c)			409		412,980

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 31

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Credit-Based Asset Servicing & Securitization LLC
Series 2006-MH1, Class B1, 6.25%, 10/25/36(a)(c)	USD		852	$	872,066
Series 2006-SL1, Class A2, 6.06%, 09/25/36(a)(c)			2,951		292,684
Series 2007-CB6, Class A4, (1 mo. LIBOR US + 0.34%), 0.45%, 07/25/37(a)(d)			563		453,330
Cumberland Park CLO Ltd.
Series 2015-2A, Class CR, (3 mo. LIBOR US + 1.80%), 2.02%, 07/20/28(a)(d)			1,190		1,193,209
Series 2015-2A, Class DR, (3 mo. LIBOR US + 2.70%), 2.92%, 07/20/28(a)(d)			500		494,911
CVC Cordatus Loan Fund VI DAC, Series 6X, Class CR, (3 mo. EURIBOR + 1.60%), 1.60%, 04/15/32(d)	EUR		1,160		1,339,001
CVC Cordatus Loan Fund XVIII DAC, Series 18X, Class E, (3 mo. EURIBOR + 5.83%), 5.83%, 04/29/34(d)			760		874,852
CWHEQ Home Equity Loan Trust, Series 2006-S5, Class A5, 6.16%, 06/25/35	USD		265		313,303
CWHEQ Revolving Home Equity Loan Resuritization Trust
Series 2006-RES, Class 4Q1B, (1 mo. LIBOR US + 0.30%), 0.41%, 12/15/33(a)(d)			576		524,574
Series 2006-RES, Class 5B1A, (1 mo. LIBOR US + 0.19%), 0.30%, 05/15/35(a)(d)			191		184,448
Series 2006-RES, Class 5B1B, (1 mo. LIBOR US + 0.19%), 0.30%, 05/15/35(a)(b)(d)			132		125,424
CWHEQ Revolving Home Equity Loan Trust
Series 2005-B, Class 2A, (1 mo. LIBOR US + 0.18%), 0.29%, 05/15/35(d)			334		327,479
Series 2006-C, Class 2A, (1 mo. LIBOR US + 0.18%), 0.29%, 05/15/36(d)			1,979		1,925,540
Series 2006-H, Class 1A, (1 mo. LIBOR US + 0.15%), 0.26%, 11/15/36(d)			1,261		1,092,185
Dartry Park CLO DAC, Series 1A, Class CRR, (3 mo. EURIBOR + 3.35%), 3.35%, 01/28/34(a)(b)(d)	EUR		500		586,350
Deer Creek CLO Ltd., Series 2017-1A, Class A, (3 mo. LIBOR US + 1.18%), 1.40%, 10/20/30(a)(d)	USD		5,561		5,567,343
Dorchester Park CLO DAC, Series 2015-1A, Class BR, (3 mo. LIBOR US + 1.45%), 1.67%, 04/20/28(a)(d)			3,064		3,052,049
Dryden 43 Senior Loan Fund
Series 2016-43A, Class AR, (3 mo. LIBOR US + 1.14%), 1.36%, 07/20/29(a)(d)			7,230		7,226,276
Series 2016-43A, Class AR2, (3 mo. LIBOR US + 1.04%), 0.00%, 04/20/34(a)(d)			5,540		5,540,000
Dryden 45 Senior Loan Fund, Series 2016-45A, Class BR, (3 mo. LIBOR US + 1.70%), 1.94%, 10/15/30(a)(d)			350		349,443
Dryden 49 Senior Loan Fund, Series 2017-49A, Class BR, (3 mo. LIBOR US + 1.60%), 0.00%, 07/18/30(a)(d)			500		500,000
Dryden 50 Senior Loan Fund, Series 2017-50A, Class B, (3 mo. LIBOR US + 1.65%), 1.89%, 07/15/30(a)(d)			450		450,113

Security		Par (000)		Value
Asset-Backed Securities (continued)
Dryden 53 CLO Ltd., Series 2017-53A, Class A, (3 mo. LIBOR US + 1.12%), 1.36%, 01/15/31(a)(d)	USD		18,720	$	18,720,578
Dryden 76 CLO Ltd., Series 2019-76A, Class A1, (3 mo. LIBOR US + 1.33%), 1.55%, 10/20/32(a)(d)			750		751,285
Dryden 77 CLO Ltd., Series 2020-77A, Class D1, (3 mo. LIBOR US + 5.14%), 5.32%, 05/20/31(a)(d)			750		752,958
Dryden XXV Senior Loan Fund
Series 2012-25A, Class ARR, (3 mo. LIBOR US + 0.90%), 1.14%, 10/15/27(a)(d)			8,399		8,402,822
Series 2012-25A, Class CRR, (3 mo. LIBOR US + 1.85%), 2.09%, 10/15/27(a)(d)			1,340		1,338,977
Dryden XXVI Senior Loan Fund, Series 2013- 26A, Class AR, (3 mo. LIBOR US + 0.90%), 1.14%, 04/15/29(a)(d)			1,170		1,170,214
Dryden XXVIII Senior Loan Fund, Series 2013- 28A, Class A1LR, (3 mo. LIBOR US + 1.20%), 1.39%, 08/15/30(a)(d)			9,085		9,078,531
Eaton Vance CLO Ltd., Series 2018-1A, Class C, (3 mo. LIBOR US + 2.20%), 2.44%, 10/15/30(a)(d)			3,550		3,540,002
Elmwood CLO II Ltd.
Series 2019-2A, Class A, (3 mo. LIBOR US + 1.45%), 1.67%, 04/20/31(a)(d)			4,020		4,020,654
Series 2019-2A, Class AR, (3 mo. LIBOR US + 1.15%), 0.00%, 04/20/34(a)(d)			3,750		3,750,000
Series 2019-2A, Class BR, (3 mo. LIBOR US + 1.65%), 0.00%, 04/20/34(a)(d)			500		500,000
Series 2019-2A, Class C, (3 mo. LIBOR US + 2.90%), 3.12%, 04/20/31(a)(d)			750		750,808
Series 2019-2A, Class D, (3 mo. LIBOR US + 3.95%), 4.17%, 04/20/31(a)(d)			1,450		1,451,060
Series 2019-2A, Class ER, (3 mo. LIBOR US + 6.80%), 0.00%, 04/20/34(a)(d)			500		500,000
Elmwood CLO III Ltd., Series 2019-3A, Class D, (3 mo. LIBOR US + 3.85%), 4.09%, 10/15/32(a)(d)			250		251,323
Elmwood CLO V Ltd.
Series 2020-2A, Class B, (3 mo. LIBOR US + 2.20%), 2.42%, 07/24/31(a)(d)			2,880		2,897,272
Series 2020-2A, Class C, (3 mo. LIBOR US + 2.75%), 2.97%, 07/24/31(a)(d)			2,880		2,875,332
Euro-Galaxy III CLO BV
Series 2013-3A, Class CRRR, (3 mo. EURIBOR + 2.35%), 2.35%, 04/24/34(a)(d)	EUR		1,200		1,407,240
Series 2013-3A, Class DRRR, (3 mo. EURIBOR + 3.25%), 3.25%, 04/24/34(a)(d)			1,585		1,858,730
FBR Securitization Trust, Series 2005-5, Class M2, (1 mo. LIBOR US + 0.71%), 0.81%, 11/25/35(d)	USD		6,465		6,342,155
First Franklin Mortgage Loan Trust
Series 2004-FFH3, Class M3, (1 mo. LIBOR US + 1.05%), 1.16%, 10/25/34(d)			1,000		974,187
Series 2006-FF13, Class A1, (1 mo. LIBOR US + 0.24%), 0.35%, 10/25/36(d)			2,340		1,865,946
Series 2006-FF13, Class A2C, (1 mo. LIBOR US + 0.32%), 0.43%, 10/25/36(d)			1,572		1,279,403
Series 2006-FF16, Class 2A3, (1 mo. LIBOR US + 0.14%), 0.25%, 12/25/36(d)			11,449		6,674,447

32 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
First Franklin Mortgage Loan Trust
Series 2006-FF17, Class A5, (1 mo. LIBOR US + 0.15%), 0.26%, 12/25/36(d)	USD		14,944	$	13,985,030
Series 2006-FFH1, Class M2, (1 mo. LIBOR US + 0.60%), 0.71%, 01/25/36(d)			2,658		2,342,898
FirstKey Homes Trust, Series 2020-SFR1, Class F1, 3.64%, 09/17/25(a)			2,690		2,766,245
Flatiron CLO 19 Ltd., Series 2019-1A, Class D, (3 mo. LIBOR US + 3.90%), 4.09%, 11/16/32(a)(d)			650		654,135
Flatiron CLO Ltd., Series 2015-1A, Class AR, (3 mo. LIBOR US + 0.89%), 1.13%, 04/15/27(a)(d)			1,195		1,195,129
Fremont Home Loan Trust, Series 2006-3, Class 1A1, (1 mo. LIBOR US + 0.28%), 0.39%, 02/25/37(d)			2,708		2,215,680
Galaxy XV CLO Ltd., Series 2013-15A, Class AR, (3 mo. LIBOR US + 1.20%), 1.44%, 10/15/30(a)(d)			1,350		1,350,545
Galaxy XXIX CLO Ltd.
Series 2018-29A, Class B, (3 mo. LIBOR US + 1.40%), 1.59%, 11/15/26(a)(d)			250		249,516
Series 2018-29A, Class C, (3 mo. LIBOR US + 1.68%), 1.87%, 11/15/26(a)(d)			1,470		1,454,213
Galaxy XXVII CLO Ltd., Series 2018-27A, Class A, (3 mo. LIBOR US + 1.02%), 1.21%, 05/16/31(a)(d)			1,000		998,004
GE-WMC Asset-Backed Pass-Through Certificates, Series 2005-2, Class A2C, (1 mo. LIBOR US + 0.50%), 0.61%, 12/25/35(d)			163		163,050
Gilbert Park CLO Ltd.
Series 2017-1A, Class C, (3 mo. LIBOR US + 1.95%), 2.19%, 10/15/30(a)(d)			3,110		3,089,448
Series 2017-1A, Class D, (3 mo. LIBOR US + 2.95%), 3.19%, 10/15/30(a)(d)			4,292		4,263,517
GoldenTree Loan Management U.S. CLO 1 Ltd.
Series 2017-1A, Class CR, (3 mo. LIBOR US + 1.85%), 2.07%, 04/20/29(a)(d)			3,120		3,119,946
Series 2017-1A, Class DR, (3 mo. LIBOR US + 2.65%), 2.87%, 04/20/29(a)(d)			1,800		1,799,939
GoldenTree Loan Management U.S. CLO3 Ltd., Series 2018-3A, Class B1, (3 mo. LIBOR US + 1.55%), 1.77%, 04/20/30(a)(d)			500		500,560
GoldenTree Loan Management U.S. CLO4 Ltd., Series 2019-4A, Class C, (3 mo. LIBOR US + 2.70%), 2.92%, 04/24/31(a)(d)			500		500,572
GoldenTree Loan Management U.S. CLO5 Ltd., Series 2019-5A, Class A, (3 mo. LIBOR US + 1.30%), 1.52%, 10/20/32(a)(d)			1,750		1,755,508
GoldenTree Loan Management U.S. CLO6 Ltd., Series 2019-6A, Class D, (3 mo. LIBOR US + 3.85%), 4.07%, 01/20/33(a)(d)			250		251,935
GoldenTree Loan Management U.S. CLO 7 Ltd.
Series 2020-7A, Class D, (3 mo. LIBOR US + 2.98%), 3.20%, 04/20/31(a)(d)			2,240		2,240,080
Series 2020-7A, Class E, (3 mo. LIBOR US + 5.50%), 5.72%, 04/20/31(a)(d)			1,000		1,000,012
GoldenTree Loan Opportunities IX Ltd.
Series 2014-9A, Class AR2, (3 mo. LIBOR US + 1.11%), 1.32%, 10/29/29(a)(d)			1,830		1,831,892

Security		Par (000)		Value
Asset-Backed Securities (continued)
GoldenTree Loan Opportunities IX Ltd.
Series 2014-9A, Class BR2, (3 mo. LIBOR US + 1.60%), 1.81%, 10/29/29(a)(d)	USD		1,000	$	1,000,960
GoldenTree Loan Opportunities X Ltd.
Series 2015-10A, Class AR, (3 mo. LIBOR US + 1.12%), 1.34%, 07/20/31(a)(d)			4,688		4,690,362
Series 2015-10A, Class DR, (3 mo. LIBOR US + 3.05%), 3.27%, 07/20/31(a)(d)			500		500,053
GoldenTree Loan Opportunities XI Ltd., Series 2015-11A, Class AR2, (3 mo. LIBOR US + 1.07%), 1.29%, 01/18/31(a)(d)			3,749		3,751,634
Golub Capital BDC 3 CLO 1 LLC, Series 2021- 1A, Class C1, (3 mo. LIBOR US + 2.80%), 0.00%, 04/15/33(a)(d)			1,250		1,240,057
Great Lakes CLO V Ltd., Series 2021-5A, Class A, (3 mo. LIBOR US + 1.70%), 0.00%, 04/15/33(a)(d)			2,540		2,540,000
Greenpoint Manufactured Housing
Series 1999-5, Class M1B, 8.29%, 12/15/29(d)			870		906,866
Series 1999-5, Class M2, 9.23%, 12/15/29(d)			889		768,049
Grippen Park CLO Ltd.
Series 2017-1A, Class A, (3 mo. LIBOR US + 1.26%), 1.48%, 01/20/30(a)(d)			1,123		1,123,633
Series 2017-1A, Class D, (3 mo. LIBOR US + 3.30%), 3.52%, 01/20/30(a)(d)			250		250,077
GSAA Home Equity Trust
Series 2005-14, Class 1A2, (1 mo. LIBOR US + 0.70%), 0.81%, 12/25/35(d)			836		363,461
Series 2006-4, Class 1A1, 2.99%, 03/25/36(d)			2,244		1,817,445
Series 2006-5, Class 2A1, (1 mo. LIBOR US + 0.14%), 0.25%, 03/25/36(d)			13		6,140
Series 2007-2, Class AF3, 5.92%, 03/25/37(d)			492		133,109
GSAMP Trust
Series 2007-H1, Class A1B, (1 mo. LIBOR US + 0.20%), 0.31%, 01/25/47(d)			916		599,243
Series 2007-HS1, Class M6, (1 mo. LIBOR US + 2.25%), 2.36%, 02/25/47(d)			1,300		1,388,739
Gulf Stream Meridian 1 Ltd.
Series 2020-IA, Class A1, (3 mo. LIBOR US + 1.37%), 1.61%, 04/15/33(a)(d)			5,820		5,835,101
Series 2020-IA, Class E, (3 mo. LIBOR US + 6.45%), 6.69%, 04/15/33(a)(d)			1,000		995,241
Gulf Stream Meridian 2 Ltd., Series 2020-IIA, Class C, (3 mo. LIBOR US + 4.85%), 5.09%, 10/15/29(a)(d)			1,500		1,508,123
Halcyon Loan Advisors Funding Ltd., Series 2015-2A, Class AR, (3 mo. LIBOR US + 1.08%), 1.30%, 07/25/27(a)(d)			4,976		4,976,354
Harvest CLO XXIII DAC, Series 23A, Class CE, (3 mo. EURIBOR + 2.05%), 2.05%, 10/20/32(a)(d)	EUR		1,430		1,664,132
Henley CLO IV DAC
Series 4A, Class C, (3 mo. EURIBOR + 2.10%), 2.10%, 04/25/34(a)(b)(d)			560		658,695
Series 4A, Class D, (3 mo. EURIBOR + 3.00%), 0.00%, 04/25/34(a)(b)(d)			750		877,326
Highbridge Loan Management Ltd.
Series 12A-18, Class A1B, (3 mo. LIBOR US + 1.25%), 1.47%, 07/18/31(a)(d)	USD		750		751,092

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 33

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Highbridge Loan Management Ltd.
Series 7A-2015, Class BR, (3 mo. LIBOR US + 1.18%), 1.37%, 03/15/27(a)(d)	USD		500	$	497,504
Home Equity Asset Trust
Series 2006-3, Class M2, (1 mo. LIBOR US + 0.60%), 0.71%, 07/25/36(d)			2,440		2,294,503
Series 2007-1, Class 2A3, (1 mo. LIBOR US + 0.30%), 0.41%, 05/25/37(d)			2,458		2,188,036
Home Equity Mortgage Loan Asset-Backed Trust
Series 2004-A, Class M2, (1 mo. LIBOR US + 2.03%), 2.13%, 07/25/34(d)			475		477,354
Series 2007-A, Class 2A2, (1 mo. LIBOR US + 0.19%), 0.30%, 04/25/37(d)			1,817		1,377,407
Home Equity Mortgage Trust, Series 2006-2, Class 1A1, 5.37%, 07/25/36(c)			2,118		432,430
Home Loan Mortgage Loan Trust, Series 2005-1, Class A3, (1 mo. LIBOR US + 0.72%), 0.83%, 04/15/36(d)			928		887,517
HPS Loan Management Ltd.
Series 10A-16, Class A1R, (3 mo. LIBOR US + 1.14%), 1.36%, 01/20/28(a)(d)			4,517		4,519,143
Series 6A-2015, Class A1R, (3 mo. LIBOR US + 1.00%), 1.20%, 02/05/31(a)(d)			11,313		11,321,676
ICG U.S. CLO Ltd., Series 2015-1A, Class A1R, (3 mo. LIBOR US + 1.14%), 1.36%, 10/19/28(a)(d)			5,294		5,295,569
Invesco Euro CLO II DAC, Series 2X, Class B1, (3 mo. EURIBOR + 1.80%), 1.80%, 08/15/32(d)	EUR		1,440		1,677,812
Invitation Homes Trust
Series 2018-SFR3, Class A, (1 mo. LIBOR US + 1.00%), 1.11%, 07/17/37(a)(d)	USD		2,681		2,685,704
Series 2018-SFR3, Class E, (1 mo. LIBOR US + 2.00%), 2.11%, 07/17/37(a)(d)			1,471		1,471,066
Irwin Home Equity Loan Trust, Series 2006-3, Class 2A3, 6.53%, 09/25/37(a)(c)			319		317,834
Jamestown CLO IX Ltd., Series 2016-9A, Class BR, (3 mo. LIBOR US + 2.65%), 2.87%, 10/20/28(a)(d)			1,830		1,826,752
JPMorgan Mortgage Acquisition Trust, Series 2006-CW1, Class M1, (1 mo. LIBOR US + 0.41%), 0.51%, 05/25/36(d)			1,170		1,146,255
Kayne CLO 5 Ltd., Series 2019-5A, Class A, (3 mo. LIBOR US + 1.35%), 1.57%, 07/24/32(a)(d)			3,770		3,773,436
Kayne CLO II Ltd., Series 2018-2A, Class AR, (3 mo. LIBOR US + 1.08%), 1.23%, 10/15/31(a)(b)(d)			3,255		3,255,000
Kayne CLO III Ltd., Series 2019-3A, Class D, (3 mo. LIBOR US + 3.95%), 4.19%, 04/15/32(a)(d)			250		250,105
KKR CLO 16 Ltd., Series 16, Class A1R, (3 mo. LIBOR US + 1.25%), 1.47%, 01/20/29(a)(d)			7,421		7,422,779
LCM 26 Ltd., Series 26A, Class A1, (3 mo. LIBOR US + 1.07%), 1.29%, 01/20/31(a)(d)			8,120		8,120,554
LCM XIV LP, Series 14A, Class AR, (3 mo. LIBOR US + 1.04%), 1.26%, 07/20/31(a)(d)			500		500,189
LCM XX LP
Series 20A, Class AR, (3 mo. LIBOR US + 1.04%), 1.26%, 10/20/27(a)(d)			3,320		3,320,897

Security		Par (000)		Value
Asset-Backed Securities (continued)
LCM XX LP
Series 20A, Class BR, (3 mo. LIBOR US + 1.55%), 1.77%, 10/20/27(a)(d)	USD		250	$	249,997
LCM XXI LP, Series 21A, Class AR, (3 mo. LIBOR US + 0.88%), 1.10%, 04/20/28(a)(d)			2,995		2,995,465
Legacy Mortgage Asset Trust
Series 2019-SL2, Class A, 3.38%, 02/25/59(a)(b)(d)			7,390		7,412,132
Series 2019-SL2, Class B, 0.00%, 02/25/59(a)(b)			2,213		331,994
Series 2019-SL2, Class M, 4.25%, 02/25/59(a)(b)(d)			2,083		2,075,710
Lehman ABS Manufactured Housing Contract Trust
Series 2001-B, Class M1, 6.63%, 04/15/40(d)			3,779		4,016,650
Series 2002-A, Class C, 0.00%, 06/15/33			319		285,527
Lehman ABS Mortgage Loan Trust, Series 2007-1, Class 2A1, (1 mo. LIBOR US + 0.09%), 0.20%, 06/25/37(a)(d)			416		324,898
Lendmark Funding Trust, Series 2019-2A, Class A, 2.78%, 04/20/28(a)			12,230		12,568,158
Litigation Fee Residual Funding LLC, Series 2015-1, Class A, 4.00%, 10/01/27(a)(b)			1,279		1,278,822
LoanCore Issuer Ltd., Series 2018-CRE1, Class A, (1 mo. LIBOR US + 1.13%), 1.24%, 05/15/28(a)(d)			1,207		1,206,849
Loanpal Solar Loan Ltd.
Series 2020-2GF, Class A, 2.75%, 07/20/47(a)			7,081		7,175,114
Series 2021-1GS, Class A, 2.29%, 01/20/48(a)			7,204		7,204,500
Long Beach Mortgage Loan Trust
Series 2006-5, Class 2A3, (1 mo. LIBOR US + 0.30%), 0.41%, 06/25/36(d)			3,640		2,227,413
Series 2006-7, Class 2A3, (1 mo. LIBOR US + 0.16%), 0.27%, 08/25/36(d)			9,661		5,189,087
Madison Avenue Manufactured Housing Contract Trust, Series 2002-A, Class B2, (1 mo. LIBOR US + 3.25%), 3.36%, 03/25/32(d)			854		858,498
Madison Park Funding X Ltd., Series 2012-10A, Class AR3, (3 mo. LIBOR US + 1.01%), 1.21%, 01/20/29(a)(d)			9,500		9,500,922
Madison Park Funding XI Ltd., Series 2013- 11A, Class AR2, (3 mo. LIBOR US + 0.90%), 1.01%, 07/23/29(a)(d)			5,363		5,363,000
Madison Park Funding XIII Ltd.
Series 2014-13A, Class AR2, (3 mo. LIBOR US + 0.95%), 1.17%, 04/19/30(a)(d)			7,780		7,776,333
Series 2014-13A, Class BR2, (3 mo. LIBOR US + 1.50%), 1.72%, 04/19/30(a)(d)			4,540		4,521,125
Madison Park Funding XIX Ltd.
Series 2015-19A, Class A1R2, (3 mo. LIBOR US + 0.92%), 1.14%, 01/22/28(a)(d)			7,698		7,699,398
Series 2015-19A, Class A2R2, (3 mo. LIBOR US + 1.50%), 1.72%, 01/22/28(a)(d)			1,000		999,003
Madison Park Funding XVI Ltd., Series 2015- 16A, Class A2R, (3 mo. LIBOR US + 1.90%), 2.12%, 04/20/26(a)(d)			500		501,034
Madison Park Funding XVIII Ltd., Series 2015- 18A, Class A1R, (3 mo. LIBOR US + 1.19%), 1.41%, 10/21/30(a)(d)			14,970		14,977,494

34 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Madison Park Funding XXII Ltd., Series 2016- 22A, Class A1R, (3 mo. LIBOR US + 1.26%), 1.50%, 01/15/33(a)(d)	USD		3,000	$	3,005,888
Madison Park Funding XXIII Ltd.
Series 2017-23A, Class A, (3 mo. LIBOR US + 1.21%), 1.42%, 07/27/30(a)(d)			750		750,188
Series 2017-23A, Class B, (3 mo. LIBOR US + 1.70%), 1.91%, 07/27/30(a)(d)			750		749,158
Madison Park Funding XXV Ltd.
Series 2017-25A, Class A2, (3 mo. LIBOR US + 1.75%), 1.97%, 04/25/29(a)(d)			550		550,544
Series 2017-25A, Class A2R, (3 mo. LIBOR US + 1.65%), 0.00%, 04/25/29(a)(d)			1,430		1,430,000
Madison Park Funding XXVI Ltd., Series 2017- 26A, Class AR, (3 mo. LIBOR US + 1.20%), 1.41%, 07/29/30(a)(d)			11,115		11,112,773
Madison Park Funding XXXI Ltd., Series 2018- 31A, Class B, (3 mo. LIBOR US + 1.70%), 1.92%, 01/23/31(a)(d)			250		250,188
Madison Park Funding XXXVI Ltd., Series 2019-36A, Class B1, (3 mo. LIBOR US + 1.85%), 2.09%, 01/15/33(a)(d)			2,470		2,486,233
Marble Point CLO XI Ltd., Series 2017-2A, Class A, (3 mo. LIBOR US + 1.18%), 1.40%, 12/18/30(a)(d)			2,000		1,999,000
Mariner CLO LLC
Series 2016-3A, Class BR2, (3 mo. LIBOR US + 1.50%), 1.72%, 07/23/29(a)(b)(d)			1,978		1,978,593
Series 2016-3A, Class CR2, (3 mo. LIBOR US + 2.05%), 2.27%, 07/23/29(a)(b)(d)			5,162		5,164,065
Series 2016-3A, Class DR2, (3 mo. LIBOR US + 2.90%), 3.12%, 07/23/29(a)(b)(d)			500		499,450
Mariner Finance Issuance Trust
Series 2019-AA, Class A, 2.96%, 07/20/32(a)			14,870		15,202,102
Series 2019-AA, Class B, 3.51%, 07/20/32(a)			2,420		2,488,320
Series 2019-AA, Class C, 4.01%, 07/20/32(a)			2,150		2,182,449
Series 2020-AA, Class A, 2.19%, 08/21/34(a)			7,050		7,155,104
Series 2020-AA, Class B, 3.21%, 08/21/34(a)			1,630		1,677,304
Series 2020-AA, Class C, 4.10%, 08/21/34(a)			1,536		1,596,844
Series 2020-AA, Class D, 5.75%, 08/21/34(a)			2,030		2,070,510
MASTR Asset-Backed Securities Trust
Series 2006-AM2, Class A4, (1 mo. LIBOR US + 0.52%), 0.63%, 06/25/36(a)(d)			1,441		1,343,597
Series 2007-HE1, Class A4, (1 mo. LIBOR US + 0.28%), 0.39%, 05/25/37(d)			1,318		1,174,146
MASTR Specialized Loan Trust,
Series 2006-3, Class A, (1 mo. LIBOR US + 0.26%), 0.37%, 06/25/46(a)(d)			457		440,835
Merrill Lynch First Franklin Mortgage Loan Trust, Series 2007-2, Class A2C, (1 mo. LIBOR US + 0.24%), 0.35%, 05/25/37(d)			1,819		1,372,448
Merrill Lynch Mortgage Investors Trust
Series 2006-OPT1, Class M1, (1 mo. LIBOR US + 0.26%), 0.37%, 08/25/37(d)			386		310,973
Series 2006-RM3, Class A2B, (1 mo. LIBOR US + 0.18%), 0.29%, 06/25/37(d)			917		279,814
MidOcean Credit CLO III, Series 2014-3A, Class A3A2, (3 mo. LIBOR US + 0.97%), 1.19%, 04/21/31(a)(d)			1,987		1,983,058
Mill City Solar Loan Ltd., Series 2019-2GS, Class A, 3.69%, 07/20/43(a)			6,482		6,837,568

Security		Par (000)		Value
Asset-Backed Securities (continued)
Morgan Stanley ABS Capital I, Inc. Trust
Series 2005-HE1, Class A2MZ, (1 mo. LIBOR US + 0.60%), 0.71%, 12/25/34(d)	USD		820	$	774,382
Series 2005-HE5, Class M4, (1 mo. LIBOR US + 0.87%), 0.98%, 09/25/35(d)			3,821		2,710,321
Series 2007-SEA1, Class 2A1, (1 mo. LIBOR US + 1.90%), 2.01%, 02/25/47(a)(d)			1,203		1,153,651
Morgan Stanley Home Equity Loan Trust, Series 2006-3, Class A3, (1 mo. LIBOR US + 0.32%), 0.43%, 04/25/36(d)			1,880		1,531,623
Morgan Stanley Mortgage Loan Trust
Series 2006-16AX, Class 1A, (1 mo. LIBOR US + 0.17%), 0.28%, 11/25/36(d)			4,089		1,222,721
Series 2007-9SL, Class A, (1 mo. LIBOR US + 0.64%), 0.75%, 07/25/37(d)			860		816,232
Mosaic Solar Loan Trust
Series 2018-2GS, Class A, 4.20%, 02/22/44(a)			2,618		2,846,232
Series 2019-2A, Class A, 2.88%, 09/20/40(a)			828		864,282
Series 2020-1A, Class A, 2.10%, 04/20/46(a)			1,411		1,424,038
Series 2020-1A, Class B, 3.10%, 04/20/46(a)			2,132		2,222,442
Mountain Hawk II CLO Ltd., Series 2013-2A, Class BR, (3 mo. LIBOR US + 1.60%), 1.82%, 07/20/24(a)(d)			165		165,244
MP CLO III Ltd., Series 2013-1A, Class AR, (3 mo. LIBOR US + 1.25%), 1.47%, 10/20/30(a)(d)			2,820		2,820,752
MP CLO VII Ltd.
Series 2015-1A, Class ARR, (3 mo. LIBOR US + 1.08%), 1.30%, 10/18/28(a)(d)			487		486,939
Series 2015-1A, Class BRR, (3 mo. LIBOR US + 1.60%), 1.82%, 10/18/28(a)(d)			750		741,889
MP CLO VIII Ltd.
Series 2015-2A, Class AR, (3 mo. LIBOR US + 0.91%), 1.13%, 10/28/27(a)(d)			4,637		4,635,901
Series 2015-2A, Class BR, (3 mo. LIBOR US + 1.42%), 1.64%, 10/28/27(a)(d)			3,250		3,202,399
Nationstar HECM Loan Trust, Series 2020-1A, Class M3, 2.82%, 09/25/30(a)(d)			2,151		2,155,719
Nationstar Home Equity Loan Trust, Series 2007-B, Class M1, (1 mo. LIBOR US + 0.41%), 0.52%, 04/25/37(d)			3,320		3,060,939
Navient Private Education Loan Trust, Series 2014-AA, Class B, 3.50%, 08/15/44(a) .			6,000		6,132,805
Navient Private Education Refi Loan Trust
Series 2020-A, Class A2B, (1 mo. LIBOR US + 0.90%), 1.01%, 11/15/68(a)(d)			2,410		2,401,652
Series 2020-FA, Class B, 2.69%, 07/15/69(a)			2,590		2,569,106
Neuberger Berman CLO XVII Ltd.
Series 2014-17A, Class BR2, (3 mo. LIBOR US + 1.50%), 1.72%, 04/22/29(a)(d)			1,500		1,501,642
Series 2014-17A, Class CR2, (3 mo. LIBOR US + 2.00%), 2.22%, 04/22/29(a)(d)			1,900		1,897,676
Neuberger Berman CLO XVI-S Ltd.,
Series 2017-16SA, Class AR, (3 mo. LIBOR US + 1.04%), 1.24%, 04/15/34(a)(d)			2,690		2,690,000
Neuberger Berman CLO XX Ltd.
Series 2015-20A, Class AR, (3 mo. LIBOR US + 0.80%), 1.04%, 01/15/28(a)(d)			850		848,649
Series 2015-20A, Class BR, (3 mo. LIBOR US + 1.25%), 1.49%, 01/15/28(a)(d)			750		746,876

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 35

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Neuberger Berman CLO XXIII Ltd., Series 2016-23A, Class BR, (3 mo. LIBOR US + 1.55%), 1.77%, 10/17/27(a)(d)	USD		400	$	399,066
Neuberger Berman Loan Advisers CLO 26 Ltd.
Series 2017-26A, Class A, (3 mo. LIBOR US + 1.17%), 1.39%, 10/18/30(a)(d)			5,520		5,521,559
Series 2017-26A, Class B, (3 mo. LIBOR US + 1.50%), 1.72%, 10/18/30(a)(d)			250		249,595
Neuberger Berman Loan Advisers CLO 37 Ltd., Series 2020-37A, Class B, (3 mo. LIBOR US + 2.20%), 2.42%, 07/20/31(a)(b)(d)			1,000		1,002,300
Neuberger Berman Loan Advisers CLO 39 Ltd., Series 2020-39A, Class E, (3 mo. LIBOR US + 7.20%), 7.44%, 01/20/32(a)(d)			250		250,367
New Century Home Equity Loan Trust, Series 2005-C, Class M2, (1 mo. LIBOR US + 0.68%), 0.56%, 12/25/35(d)			2,166		1,971,683
Nomura Asset Acceptance Corp. Alternative Loan Trust, Series 2006-S5, Class A1, (1 mo. LIBOR US + 0.40%), 0.51%, 10/25/36(a)(d)			203		223,320
Oaktree CLO Ltd.
Series 2014-1A, Class A2R, (3 mo. LIBOR US + 1.85%), 2.04%, 05/13/29(a)(d)			1,840		1,830,075
Series 2015-1A, Class A1R, (3 mo. LIBOR US + 0.87%), 1.09%, 10/20/27(a)(d)			324		324,187
Oaktree EIF III Series I Ltd., Series 2016-IIIA, Class B, (3 mo. LIBOR US + 2.00%), 2.22%, 10/20/27(a)(d)			425		425,482
Oakwood Mortgage Investors, Inc.
Series 2001-D, Class A2, 5.26%, 01/15/19(d)			637		436,505
Series 2001-D, Class A4, 6.93%, 09/15/31(d)			405		321,602
Series 2002-B, Class M1, 7.62%, 06/15/32(d)			4,483		3,804,350
Ocean Trails CLO VI
Series 2016-6A, Class BRR, (3 mo. LIBOR US + 1.45%), 0.00%, 07/15/28(a)(d)			1,055		1,055,000
Series 2016-6A, Class CRR, (3 mo. LIBOR US + 2.25%), 0.00%, 07/15/28(a)(d)			1,750		1,750,000
OCP CLO Ltd.
Series 2013-4A, Class A2RR, (3 mo. LIBOR US + 1.45%), 1.67%, 04/24/29(a)(d)			2,500		2,460,357
Series 2013-4A, Class BRR, (3 mo. LIBOR US + 1.90%), 2.12%, 04/24/29(a)(d)			4,618		4,486,134
Series 2013-4A, Class CRR, (3 mo. LIBOR US + 3.00%), 3.22%, 04/24/29(a)(d)			3,000		2,934,056
Series 2014-5A, Class A1R, (3 mo. LIBOR US + 1.08%), 1.30%, 04/26/31(a)(d)			660		660,016
Series 2014-5A, Class A2R, (3 mo. LIBOR US + 1.40%), 1.62%, 04/26/31(a)(d)			1,070		1,055,911
Series 2014-7A, Class A2RR, (3 mo. LIBOR US + 1.65%), 1.87%, 07/20/29(a)(d)			1,000		990,643
Series 2015-10A, Class A1R, (3 mo. LIBOR US + 0.82%), 1.04%, 10/26/27(a)(d)			346		345,787
Series 2015-10A, Class BR, (3 mo. LIBOR US + 1.85%), 2.07%, 10/26/27(a)(d)			1,420		1,420,284
Series 2015-9A, Class BR, (3 mo. LIBOR US + 1.75%), 1.99%, 07/15/27(a)(d)			250		248,732
Series 2016-12A, Class A1R, (3 mo. LIBOR US + 1.12%), 1.34%, 10/18/28(a)(d)			9,946		9,943,961
Series 2016-12A, Class A2R, (3 mo. LIBOR US + 1.60%), 1.82%, 10/18/28(a)(d)			500		500,327
Series 2017-13A, Class A1A, (3 mo. LIBOR US + 1.26%), 1.50%, 07/15/30(a)(d)			9,170		9,171,588

Security		Par (000)		Value
Asset-Backed Securities (continued)
OCP CLO Ltd.
Series 2017-14A, Class B, (3 mo. LIBOR US + 1.95%), 2.13%, 11/20/30(a)(d)	USD		500	$	499,857
Series 2019-16A, Class ER, (3 mo. LIBOR US + 6.35%), 6.44%, 04/10/33(a)(d)			450		450,000
Series 2020-19A, Class B, (3 mo. LIBOR US + 2.50%), 2.72%, 07/20/31(a)(d)			500		504,054
Series 2020-19A, Class C, (3 mo. LIBOR US + 2.95%), 3.17%, 07/20/31(a)(d)			650		648,124
Series 2020-19A, Class D, (3 mo. LIBOR US + 4.47%), 4.69%, 07/20/31(a)(d)			525		528,113
OCP Euro CLO DAC, Series 2017-2X, Class B, (3 mo. EURIBOR + 1.35%), 1.35%, 01/15/32(d)	EUR		1,130		1,320,554
Octagon Investment Partners 18-R Ltd., Series 2018-18A, Class A1A, (3 mo. LIBOR US + 0.96%), 1.18%, 04/16/31(a)(d)	USD		7,300		7,298,517
Octagon Investment Partners 32 Ltd., Series 2017-1A, Class B1, (3 mo. LIBOR US + 1.70%), 1.94%, 07/15/29(a)(d)			1,650		1,648,581
Octagon Investment Partners 36 Ltd., Series 2018-1A, Class A1, (3 mo. LIBOR US + 0.97%), 1.21%, 04/15/31(a)(d)			250		249,663
Octagon Investment Partners 46 Ltd.
Series 2020-2A, Class B, (3 mo. LIBOR US + 2.20%), 2.44%, 07/15/33(a)(d)			3,290		3,305,453
Series 2020-2A, Class D, (3 mo. LIBOR US + 4.60%), 4.84%, 07/15/33(a)(d)			2,470		2,482,844
Octagon Investment Partners 47 Ltd., Series 2020-1A, Class E, (3 mo. LIBOR US + 6.42%), 6.64%, 04/20/31(a)(d)			1,000		999,335
Octagon Investment Partners 48 Ltd., Series 2020-3A, Class C, (3 mo. LIBOR US + 2.55%), 2.78%, 10/20/31(a)(d)			1,650		1,652,267
Octagon Investment Partners XVI Ltd., Series 2013-1A, Class A1R, (3 mo. LIBOR US + 1.02%), 1.24%, 07/17/30(a)(d)			3,580		3,571,821
Octagon Investment Partners XVII Ltd., Series 2013-1A, Class A1R2, (3 mo. LIBOR US + 1.00%), 1.22%, 01/25/31(a)(d)			7,240		7,230,243
Octagon Investment Partners XXIII Ltd., Series 2015-1A, Class CR, (3 mo. LIBOR US + 1.85%), 2.09%, 07/15/27(a)(d)			2,840		2,837,026
OHA Credit Funding 3 Ltd., Series 2019-3A, Class B1, (3 mo. LIBOR US + 1.80%), 2.02%, 07/20/32(a)(d)			2,989		2,992,754
OHA Loan Funding Ltd.
Series 2013-2A, Class AR, (3 mo. LIBOR US + 1.04%), 1.22%, 05/23/31(a)(d)			6,219		6,196,767
Series 2015-1A, Class A1R2, (3 mo. LIBOR US + 1.34%), 1.53%, 11/15/32(a)(d)			5,400		5,421,411
Series 2016-1A, Class B1R, (3 mo. LIBOR US + 1.60%), 1.82%, 01/20/33(a)(d)			250		250,339
OneMain Financial Issuance Trust
Series 2019-1A, Class E, 5.69%, 02/14/31(a)			5,010		5,084,726
Series 2019-2A, Class A, 3.14%, 10/14/36(a)			14,760		15,688,535
Series 2020-1A, Class A, 3.84%, 05/14/32(a)			12,330		12,936,153
Series 2020-2A, Class C, 2.76%, 09/14/35(a)			2,620		2,689,486
Series 2020-2A, Class D, 3.45%, 09/14/35(a)			6,620		6,988,197

36 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Option One Mortgage Acceptance Corp. Asset- Backed Certificates, Series 2003-4, Class A2, (1 mo. LIBOR US + 0.64%), 0.75%, 07/25/33(d)	USD		779	$	745,645
Option One Mortgage Loan Trust
Series 2006-3, Class 1A1, (1 mo. LIBOR US + 0.14%), 0.25%, 02/25/37(d)			1,193		909,340
Series 2007-CP1, Class 2A3, (1 mo. LIBOR US + 0.21%), 0.32%, 03/25/37(d)			2,360		1,903,039
Series 2007-FXD1, Class 1A1, 5.87%, 01/25/37(c)			2,492		2,454,038
Series 2007-FXD1, Class 2A1, 5.87%, 01/25/37(c)			6,219		6,155,947
Series 2007-FXD2, Class 1A1, 5.82%, 03/25/37(c)			3,315		3,312,984
Option One Mortgage Loan Trust Asset-Backed Certificates, Series 2005-4, Class M3, (1 mo. LIBOR US + 0.74%), 0.84%, 11/25/35(d)			4,030		3,771,756
Origen Manufactured Housing Contract Trust
Series 2001-A, Class M1, 7.82%, 03/15/32(d)			1,244		1,216,601
Series 2007-B, Class A1, (1 mo. LIBOR US + 1.20%), 1.31%, 10/15/37(a)(b)(d)			1,513		1,487,519
Ownit Mortgage Loan Trust Series, Series 2006-2, Class A2C, 6.50%, 01/25/37(c)			1,990		1,900,574
OZLM Funding III Ltd., Series 2013-3A, Class BRR, (3 mo. LIBOR US + 2.70%), 2.92%, 01/22/29(a)(d)			4,720		4,719,834
OZLM Funding IV Ltd.
Series 2013-4A, Class A1R, (3 mo. LIBOR US + 1.25%), 1.47%, 10/22/30(a)(d)			13,035		13,029,333
Series 2013-4A, Class A2R, (3 mo. LIBOR US + 1.70%), 1.92%, 10/22/30(a)(d)			2,120		2,123,369
OZLM VI Ltd., Series 2014-6A, Class A2AS, (3 mo. LIBOR US + 1.75%), 1.97%, 04/17/31(a)(d)			900		900,528
OZLM VIII Ltd., Series 2014-8A, Class BRR, (3 mo. LIBOR US + 2.20%), 2.42%, 10/17/29(a)(d)			1,160		1,157,682
OZLM XII Ltd., Series 2015-12A, Class A2R, (3 mo. LIBOR US + 1.60%), 1.81%, 04/30/27(a)(d)			500		498,195
OZLM XIV Ltd., Series 2015-14A, Class A2AR, (3 mo. LIBOR US + 1.70%), 1.94%, 01/15/29(a)(d)			5,770		5,745,113
OZLM XIX Ltd., Series 2017-19A, Class A1, (3 mo. LIBOR US + 1.22%), 1.46%, 11/22/30(a)(d)			2,160		2,160,001
OZLM XVIII Ltd., Series 2018-18A, Class A, (3 mo. LIBOR US + 1.02%), 1.26%, 04/15/31(a)(d)			2,620		2,618,692
OZLM XX Ltd., Series 2018-20A, Class A2, (3 mo. LIBOR US + 1.65%), 1.87%, 04/20/31(a)(d)			600		599,483
OZLM XXI Ltd., Series 2017-21A, Class B, (3 mo. LIBOR US + 1.90%), 2.12%, 01/20/31(a)(d)			930		930,551
OZLM XXIV Ltd., Series 2019-24A, Class A2A, (3 mo. LIBOR US + 2.25%), 2.47%, 07/20/32(a)(d)			750		754,260

Security		Par (000)		Value
Asset-Backed Securities (continued)
Palmer Square CLO Ltd.
Series 2014-1A, Class A1R2, (3 mo. LIBOR US + 1.13%), 1.35%, 01/17/31(a)(d)	USD		4,548	$	4,548,207
Series 2015-1A, Class A1R3, (3 mo. LIBOR US + 1.00%), 1.24%, 05/21/29(a)(d)			10,965		10,969,069
Series 2015-1A, Class A2R3, (3 mo. LIBOR US + 1.40%), 1.64%, 05/21/29(a)(d)			2,460		2,461,657
Series 2015-2A, Class A2R2, (3 mo. LIBOR US + 1.55%), 1.77%, 07/20/30(a)(d)			2,500		2,503,191
Series 2015-2A, Class CR2, (3 mo. LIBOR US + 2.75%), 2.97%, 07/20/30(a)(d)			1,000		985,178
Series 2018-1A, Class A1, (3 mo. LIBOR US + 1.03%), 1.25%, 04/18/31(a)(d)			3,360		3,361,976
Series 2018-2A, Class A1A, (3 mo. LIBOR US + 1.10%), 1.32%, 07/16/31(a)(d)			4,820		4,820,124
Series 2018-2A, Class A2, (3 mo. LIBOR US + 1.65%), 1.87%, 07/16/31(a)(d)			1,500		1,502,233
Series 2018-3A, Class A2, (3 mo. LIBOR US + 1.35%), 1.54%, 08/15/26(a)(d)			3,323		3,324,399
Series 2018-3A, Class B, (3 mo. LIBOR US + 1.90%), 2.09%, 08/15/26(a)(d)			1,650		1,631,892
Series 2019-1A, Class C, (3 mo. LIBOR US + 3.75%), 3.94%, 11/14/32(a)(d)			350		351,893
Palmer Square Loan Funding Ltd.
Series 2018-4A, Class A2, (3 mo. LIBOR US + 1.45%), 1.64%, 11/15/26(a)(d)			700		700,612
Series 2018-4A, Class D, (3 mo. LIBOR US + 4.25%), 4.44%, 11/15/26(a)(d)			1,000		979,535
Series 2018-5A, Class A2, (3 mo. LIBOR US + 1.40%), 1.62%, 01/20/27(a)(d)			3,217		3,218,470
Series 2018-5A, Class D, (3 mo. LIBOR US + 4.25%), 4.47%, 01/20/27(a)(d)			800		777,489
Series 2019-1A, Class D, (3 mo. LIBOR US + 5.80%), 6.02%, 04/20/27(a)(d)			2,050		2,067,773
Series 2019-2A, Class B, (3 mo. LIBOR US + 2.25%), 2.47%, 04/20/27(a)(d)			2,340		2,336,782
Series 2019-2A, Class C, (3 mo. LIBOR US + 3.25%), 3.47%, 04/20/27(a)(d)			250		250,056
Series 2019-2A, Class D, (3 mo. LIBOR US + 5.50%), 5.72%, 04/20/27(a)(d)			1,500		1,504,490
Series 2019-3A, Class A2, (3 mo. LIBOR US + 1.60%), 1.78%, 08/20/27(a)(d)			2,610		2,610,435
Series 2019-3A, Class B, (3 mo. LIBOR US + 2.10%), 2.28%, 08/20/27(a)(d)			1,940		1,936,852
Series 2019-4A, Class B, (3 mo. LIBOR US + 2.10%), 2.32%, 10/24/27(a)(d)			1,460		1,457,492
Series 2019-4A, Class D, (3 mo. LIBOR US + 5.90%), 6.12%, 10/24/27(a)(d)			3,013		3,021,970
Series 2020-1A, Class A2, (3 mo. LIBOR US + 1.35%), 1.53%, 02/20/28(a)(d)			4,860		4,862,691
Series 2020-1A, Class C, (3 mo. LIBOR US + 2.50%), 2.68%, 02/20/28(a)(d)			375		375,935
Series 2020-2A, Class A2, (3 mo. LIBOR US + 1.55%), 1.77%, 04/20/28(a)(d)			5,850		5,856,389
Series 2020-2A, Class B, (3 mo. LIBOR US + 2.25%), 2.47%, 04/20/28(a)(d)			1,000		1,000,469
Series 2020-2A, Class C, (3 mo. LIBOR US + 3.00%), 3.22%, 04/20/28(a)(d)			1,000		1,000,083
Series 2020-4A, Class A2, (3 mo. LIBOR US + 1.60%), 1.79%, 11/25/28(a)(d)			2,640		2,648,610
Series 2020-4A, Class C, (3 mo. LIBOR US + 3.60%), 3.79%, 11/25/28(a)(d)			500		502,580

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 37

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Palmer Square Loan Funding Ltd.
Series 2021-1A, Class D, 6.16%, 04/20/29(a)(d)	USD		500	$	501,355
Series 2021-2A, Class D, (3 mo. LIBOR US + 5.00%), 0.00%, 05/20/29(a)(d)			500		500,000
Parallel Ltd.
Series 2015-1A, Class AR, (3 mo. LIBOR US + 0.85%), 1.07%, 07/20/27(a)(d)			1,816		1,816,368
Series 2015-1A, Class C1R, (3 mo. LIBOR US + 1.75%), 1.97%, 07/20/27(a)(d)			1,150		1,117,422
Park Avenue Institutional Advisers CLO Ltd.
Series 2017-1A, Class A1R, (3 mo. LIBOR US + 1.24%), 1.44%, 02/14/34(a)(d)			6,400		6,411,276
Series 2017-1A, Class A2R, (3 mo. LIBOR US + 1.55%), 1.75%, 02/14/34(a)(d)			4,450		4,413,524
Series 2019-1A, Class A1, (3 mo. LIBOR US + 1.48%), 1.67%, 05/15/32(a)(d)			500		505,422
Series 2019-1A, Class A2A, (3 mo. LIBOR US + 2.00%), 2.19%, 05/15/32(a)(d)			500		499,996
PPM CLO 4 Ltd., Series 2020-4A, Class B, (3 mo. LIBOR US + 1.90%), 2.10%, 10/18/31(a)(d)			750		751,788
Preston Ridge Partners Mortgage LLC, Series 2020-4, Class A1, 2.95%, 10/25/25(a)(c)			8,819		8,843,970
Pretium Mortgage Credit Partners I LLC, Series 2020-NPL2, Class A1, 3.72%, 02/27/60(a)(c)			13,754		13,873,272
Progress Residential, Series 2021-SFR1, Class F, 2.76%, 04/17/38(a)			2,900		2,844,720
Progress Residential Trust
Series 2017-SFR1, Class A, 2.77%, 08/17/34(a)			2,633		2,649,208
Series 2018-SFR2, Class F, 4.95%, 08/17/35(a)			1,030		1,034,649
Series 2019-SFR1, Class E, 4.47%, 08/17/35(a)			2,000		2,050,833
Series 2020-SFR2, Class B, 2.58%, 06/17/37(a)			550		560,307
Series 2020-SFR2, Class D, 3.87%, 06/17/37(a)			1,886		1,942,247
Series 2020-SFR3, Class E, 2.30%, 10/17/27(a)			2,870		2,845,971
Series 2020-SFR3, Class F, 2.80%, 10/17/27(a)			5,410		5,408,342
Series 2021-SFR2, Class F, 3.40%, 04/19/38(a)			5,967		5,936,222
Race Point IX CLO Ltd.
Series 2015-9A, Class A1A2, (3 mo. LIBOR US + 0.94%), 0.00%, 10/15/30(a)(d)			4,805		4,805,000
Series 2015-9A, Class A1AR, (3 mo. LIBOR US + 1.21%), 1.45%, 10/15/30(a)(d)			3,710		3,711,194
Race Point X CLO Ltd., Series 2016-10A, Class A1R, (3 mo. LIBOR US + 1.10%), 1.32%, 07/25/31(a)(d)			5,472		5,452,503
RAMP Series Trust, Series 2004-RS7, Class A2A, (1 mo. LIBOR US + 0.62%), 0.73%, 07/25/34(d)			1,788		1,561,407
Recette CLO Ltd., Series 2015-1A, Class BRR, (3 mo. LIBOR US + 1.40%), 1.51%, 04/20/34(a)(d)			500		500,000

Security		Par (000)		Value
Asset-Backed Securities (continued)
Regatta VI Funding Ltd., Series 2016-1A, Class AR, (3 mo. LIBOR US + 1.08%), 1.30%, 07/20/28(a)(d)	USD		7,885	$	7,882,419
Regatta VII Funding Ltd., Series 2016-1A, Class BR, (3 mo. LIBOR US + 1.50%), 1.69%, 12/20/28(a)(d)			250		246,653
Regatta XIII Funding Ltd., Series 2018-2A, Class C, (3 mo. LIBOR US + 3.10%), 3.34%, 07/15/31(a)(d)			375		374,576
Regatta XVIII Funding Ltd., Series 2021-1A, Class B, (3 mo. LIBOR US + 1.45%), 0.00%, 01/15/34(a)(d)			750		750,000
Regional Management Issuance Trust,
Series 2019-1, Class A, 3.05%, 11/15/28(a)			12,820		13,036,190
Republic FInance Issuance Trust, Series 2019-A, Class A, 3.43%, 11/22/27(a)			14,870		15,082,672
Riserva CLO Ltd., Series 2016-3A, Class ARR, (3 mo. LIBOR US + 1.06%), 1.25%, 01/18/34(a)(d)			5,690		5,684,338
Rockford Tower CLO Ltd.
Series 2017-1A, Class AR, (3 mo. LIBOR US + 1.03%), 1.27%, 04/15/29(a)(d)			10,140		10,133,291
Series 2017-1A, Class AR2, (3 mo. LIBOR US + 1.10%), 0.00%, 04/20/34(a)(d)			11,327		11,327,000
Series 2017-1A, Class BR, (3 mo. LIBOR US + 1.45%), 1.69%, 04/15/29(a)(d)			7,210		7,115,807
Series 2017-1A, Class BR2A, (3 mo. LIBOR US + 1.65%), 0.00%, 04/20/34(a)(d)			7,079		7,079,000
Series 2017-1A, Class CR, (3 mo. LIBOR US + 1.85%), 2.09%, 04/15/29(a)(d)			2,490		2,488,281
Series 2017-1A, Class DR, (3 mo. LIBOR US + 2.65%), 2.89%, 04/15/29(a)(d)			750		741,365
Series 2017-2A, Class BR, (3 mo. LIBOR US + 1.50%), 1.74%, 10/15/29(a)(d)			8,271		8,146,035
Series 2017-2A, Class CR, (3 mo. LIBOR US + 1.90%), 2.14%, 10/15/29(a)(d)			2,750		2,716,870
Series 2017-2A, Class DR, (3 mo. LIBOR US + 2.85%), 3.09%, 10/15/29(a)(d)			4,766		4,726,130
Series 2017-2A, Class ER, (3 mo. LIBOR US + 6.25%), 6.49%, 10/15/29(a)(d)			1,750		1,733,721
Series 2017-3A, Class A, (3 mo. LIBOR US + 1.19%), 1.41%, 10/20/30(a)(d)			14,614		14,617,662
Series 2018-1A, Class A, (3 mo. LIBOR US + 1.10%), 1.28%, 05/20/31(a)(d)			1,953		1,953,960
Series 2018-1A, Class B, (3 mo. LIBOR US + 1.72%), 1.90%, 05/20/31(a)(d)			1,500		1,498,293
Series 2018-1A, Class D, (3 mo. LIBOR US + 3.00%), 3.18%, 05/20/31(a)(d)			750		729,720
Series 2018-2A, Class A, (3 mo. LIBOR US + 1.16%), 1.38%, 10/20/31(a)(d)			1,000		1,000,336
Series 2018-2A, Class B, (3 mo. LIBOR US + 1.80%), 2.02%, 10/20/31(a)(d)			500		500,819
Series 2019-2A, Class B, (3 mo. LIBOR US + 1.93%), 2.11%, 08/20/32(a)(d)			1,250		1,250,864
Rockford Tower Europe CLO DAC
Series 2018-1X, Class B, (3 mo. EURIBOR + 1.85%), 1.85%, 12/20/31(d)	EUR		3,898		4,559,791
Series 2018-1X, Class C, (3 mo. EURIBOR + 2.47%), 2.47%, 12/20/31(d)			1,805		2,104,173
Romark WM-R Ltd., Series 2018-1A, Class A1, (3 mo. LIBOR US + 1.03%), 1.25%, 04/20/31(a)(d)	USD		4,272		4,267,840

38 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
RR 10 Ltd., Series 2020-10A, Class A2B, (3 mo. LIBOR US + 3.00%), 3.24%, 07/15/33(a)(d)	USD		601	$	603,620
RR 11 Ltd.
Series 2020-11A, Class A2, (3 mo. LIBOR US + 2.10%), 2.34%, 10/15/31(a)(d)			4,176		4,200,189
Series 2020-11A, Class D, (3 mo. LIBOR US + 7.12%), 7.36%, 10/15/31(a)(d)			2,250		2,257,505
RR 2 Ltd.
Series 2017-2A, Class A2, (3 mo. LIBOR US + 1.60%), 1.84%, 10/15/29(a)(d)			750		744,354
Series 2017-2A, Class B, (3 mo. LIBOR US + 2.00%), 2.24%, 10/15/29(a)(d)			750		748,998
RR 3 Ltd., Series 2018-3A, Class A1R2, (3 mo. LIBOR US + 1.09%), 1.33%, 01/15/30(a)(d)			2,020		2,022,251
RR 4 Ltd., Series 2018-4A, Class A2, (3 mo. LIBOR US + 1.55%), 1.79%, 04/15/30(a)(d)			1,400		1,377,456
RR 5 Ltd., Series 2018-5A, Class A2, (3 mo. LIBOR US + 1.65%), 1.89%, 10/15/31(a)(d)			1,000		985,817
RRE 2 Loan Management DAC, Series 2A, Class B, (3 mo. EURIBOR + 1.80%), 1.80%, 01/15/32(a)(d)	EUR		750		880,624
SACO I Trust, Series 2006-9, Class A1, (1 mo. LIBOR US + 0.30%), 0.41%, 08/25/36(d)	USD		179		178,327
Securitized Asset Backed Receivables LLC Trust, Series 2006-OP1, Class M6, (1 mo. LIBOR US + 1.01%), 1.11%, 10/25/35(d)			340		305,200
Security National Mortgage Loan Trust, Series 2007-1A, Class 2A, (1 mo. LIBOR US + 0.35%), 0.46%, 04/25/37(a)(d)			259		259,037
SG Mortgage Securities Trust, Series 2006- FRE2, Class A2C, (1 mo. LIBOR US + 0.32%), 0.43%, 07/25/36(d)			936		292,124
Signal Peak CLO 1 Ltd.
Series 2014-1A, Class ARR, (3 mo. LIBOR US + 1.17%), 1.39%, 01/17/29(a)(d)			18,150		18,153,365
Series 2014-1A, Class BRR, (3 mo. LIBOR US + 1.75%), 1.97%, 01/17/29(a)(d)			1,950		1,950,352
Signal Peak CLO 2 LLC
Series 2015-1A, Class BR2, (3 mo. LIBOR US + 1.50%), 1.72%, 04/20/29(a)(d)			7,152		7,081,906
Series 2015-1A, Class CR2, (3 mo. LIBOR US + 1.90%), 2.12%, 04/20/29(a)(d)			2,000		2,000,634
Signal Peak CLO 4 Ltd., Series 2017-4A, Class A, (3 mo. LIBOR US + 1.21%), 1.43%, 10/26/29(a)(d)			1,800		1,801,262
Signal Peak CLO 5 Ltd., Series 2018-5A, Class A, (3 mo. LIBOR US + 1.11%), 1.33%, 04/25/31(a)(d)			3,550		3,550,182
Signal Peak CLO 8 Ltd.
Series 2020-8A, Class A, (3 mo. LIBOR US + 1.27%), 1.49%, 04/20/33(a)(d)			3,010		3,016,770
Series 2020-8A, Class B, (3 mo. LIBOR US + 1.65%), 1.87%, 04/20/33(a)(d)			1,000		1,003,175
Silver Creek CLO Ltd.
Series 2014-1A, Class AR, (3 mo. LIBOR US + 1.24%), 1.46%, 07/20/30(a)(d)			3,920		3,920,731
Series 2014-1A, Class CR, (3 mo. LIBOR US + 2.30%), 2.52%, 07/20/30(a)(d)			500		498,686
Sixth Street CLO XVIII Ltd., Series 2021-18A, Class E, (3 mo. LIBOR US + 6.50%), 6.50%, 04/20/34(a)(d)			1,500		1,500,000

Security		Par (000)		Value
Asset-Backed Securities (continued)
SLM Private Credit Student Loan Trust
Series 2004-A, Class A3, (3 mo. LIBOR US + 0.40%), 0.58%, 06/15/33(d)	USD		1,487	$	1,472,987
Series 2004-B, Class A3, (3 mo. LIBOR US + 0.33%), 0.51%, 03/15/24(d)			4,651		4,642,027
Series 2006-A, Class A5, (3 mo. LIBOR US + 0.29%), 0.47%, 06/15/39(d)			13,154		12,851,628
Series 2006-B, Class A5, (3 mo. LIBOR US + 0.27%), 0.45%, 12/15/39(d)			419		409,930
SLM Private Education Loan Trust, Series 2010-C, Class A5, (1 mo. LIBOR US + 4.75%), 4.86%, 10/15/41(a)(d)			17,610		19,081,120
SMB Private Education Loan Trust
Series 2015-B, Class B, 3.50%, 12/17/40(a)			2,480		2,561,363
Series 2020-B, Class B, 2.76%, 07/15/53(a)			2,440		2,349,628
Series 2020-PTA, Class A2A, 1.60%, 09/15/54(a)			20,680		20,802,539
Series 2020-PTA, Class B, 2.50%, 09/15/54(a)			6,740		6,534,577
Series 2021-A, Class B, 2.31%, 01/15/53(a)			4,670		4,539,466
Series 2021-A, Class C, 2.99%, 01/15/53(a)			11,470		11,267,816
Series 2021-A, Class D1, 3.86%, 01/15/53(a)			6,160		6,056,733
Series 2021-A, Class D2, 3.86%, 01/15/53(a)			3,360		3,314,064
SoFi RR Funding IV Trust, Series 2021-1, Class A, 2.98%, 12/31/25(a)(b)(c)			17,232		17,231,738
Sound Point CLO II Ltd., Series 2013-1A, Class A1R, (3 mo. LIBOR US + 1.07%), 1.29%, 01/26/31(a)(d)			825		825,216
Sound Point CLO XI Ltd., Series 2016-1A, Class CR, (3 mo. LIBOR US + 2.25%), 2.47%, 07/20/28(a)(d)			440		439,384
Sound Point CLO XV Ltd.
Series 2017-1A, Class AR, (3 mo. LIBOR US + 1.15%), 1.37%, 01/23/29(a)(d)			1,720		1,720,463
Series 2017-1A, Class ARR, (3 mo. LIBOR US + 0.90%), 1.09%, 01/23/29(a)(d)			1,440		1,440,000
Series 2017-1A, Class BR, (3 mo. LIBOR US + 1.50%), 0.00%, 01/23/29(a)(d)			350		350,000
Sound Point CLO XVIII Ltd., Series 2017-4A, Class B, (3 mo. LIBOR US + 1.80%), 2.02%, 01/21/31(a)(d)			500		488,089
Sound Point CLO XXIII, Series 2019-2A, Class A1, (3 mo. LIBOR US + 1.40%), 1.64%, 04/15/32(a)(d)			19,610		19,620,629
Sound Point CLO XXVI Ltd., Series 2020-1A, Class D, (3 mo. LIBOR US + 4.70%), 4.92%, 07/20/30(a)(d)			1,430		1,431,035
Sound Point Euro CLO I Funding DAC, Series 1X, Class B1, (3 mo. EURIBOR + 2.00%), 2.00%, 04/25/32(d)	EUR		660		771,696
Sound Point Euro CLO II Funding DAC, Series 2A, Class B1, (3 mo. EURIBOR + 1.85%), 1.85%, 10/26/32(a)(d)			3,020		3,559,697
Soundview Home Loan Trust, Series 2004- WMC1, Class M2, (1 mo. LIBOR US + 0.80%), 0.90%, 01/25/35(d)	USD		44		42,385
St. Paul’s CLO VI DAC, Series 6A, Class CRR, (3 mo. EURIBOR + 2.60%), 2.60%, 05/20/34(a)(d)	EUR		2,680		3,142,836
St. Paul’s CLO XII DAC, Series 12X, Class B1, (3 mo. EURIBOR + 1.60%), 1.60%, 04/15/33(d)			1,420		1,641,359

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 39

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
STAR Trust, Series 2021-SFR1, Class F, (1 mo. LIBOR US + 2.40%), 2.52%, 04/17/38(a)(d)	USD		1,030	$	1,032,494
Steele Creek CLO Ltd., Series 2017-1A, Class A, (3 mo. LIBOR US + 1.25%), 1.49%, 10/15/30(a)(d)			4,140		4,128,687
Stewart Park CLO Ltd., Series 2015-1A, Class CR, (3 mo. LIBOR US + 1.80%), 2.04%, 01/15/30(a)(d)			1,630		1,623,363
Stratus CLO Ltd., Series 2020-2A, Class D, (3 mo. LIBOR US + 3.65%), 3.92%, 10/15/28(a)(d)			500		500,936
Structured Asset Securities Corp. Assistance Loan Trust, Series 2003-AL2, Class A, 3.36%, 01/25/31(a)			204		203,027
Structured Asset Securities Corp. Mortgage Pass-Through Certificates, Series 2004- 23XS, Class 2A1, (1 mo. LIBOR US + 0.45%), 0.56%, 01/25/35(d)			84		84,112
Sutton Park CLO DAC, Series 1X, Class BE, (3 mo. EURIBOR + 2.35%), 2.35%, 11/15/31(d)	EUR		940		1,097,251
Symphony CLO XVII Ltd., Series 2016-17A, Class AR, (3 mo. LIBOR US + 0.88%), 1.12%, 04/15/28(a)(d)	USD		3,198		3,195,728
Symphony CLO XVIII Ltd.
Series 2016-18A, Class AR, (3 mo. LIBOR US + 1.15%), 1.37%, 01/23/28(a)(d)			4,140		4,141,114
Series 2016-18A, Class B, (3 mo. LIBOR US + 1.80%), 2.02%, 01/23/28(a)(d)			300		300,338
Symphony CLO XXI Ltd., Series 2019-21A, Class A, (3 mo. LIBOR US + 1.38%), 1.62%, 07/15/32(a)(d)			4,230		4,226,220
Symphony CLO XXVI Ltd., Series 2021-26A, Class AR, (3 mo. LIBOR US + 1.08%), 1.19%, 04/20/33(a)(b)(d)			2,377		2,377,000
TCI-Flatiron CLO Ltd.
Series 2017-1A, Class A, (3 mo. LIBOR US + 1.20%), 1.39%, 11/18/30(a)(d)			3,290		3,287,406
Series 2017-1A, Class AR, (3 mo. LIBOR US + 0.96%), 0.00%, 04/20/34(a)(d)			4,180		4,180,000
TCW CLO AMR Ltd., Series 2019-1A, Class B, (3 mo. LIBOR US + 1.68%), 1.87%, 02/15/29(a)(d)			1,650		1,651,052
TCW CLO Ltd., Series 2020-1A, Class DR, (3 mo. LIBOR US + 3.70%), 3.92%, 10/20/31(a)(d)			1,100		1,100,438
THL Credit Wind River CLO Ltd.
Series 2016-1A, Class AR, (3 mo. LIBOR US + 1.05%), 1.29%, 07/15/28(a)(d)			3,881		3,880,778
Series 2017-1A, Class C, (3 mo. LIBOR US + 2.30%), 2.52%, 04/18/29(a)(d)			1,400		1,397,382
TIAA CLO III Ltd., Series 2017-2A, Class A, (3 mo. LIBOR US + 1.15%), 1.37%, 01/16/31(a)(d)			1,467		1,467,049
TICP CLO I Ltd., Series 2015-1A, Class AR, (3 mo. LIBOR US + 0.80%), 1.02%, 07/20/27(a)(d)			639		639,000
TICP CLO IX Ltd.
Series 2017-9A, Class A, (3 mo. LIBOR US + 1.14%), 1.36%, 01/20/31(a)(d)			3,080		3,081,399
Series 2017-9A, Class B, (3 mo. LIBOR US + 1.60%), 1.82%, 01/20/31(a)(d)			450		450,452

Security		Par (000)		Value
Asset-Backed Securities (continued)
TICP CLO IX Ltd.
Series 2017-9A, Class D, (3 mo. LIBOR US + 2.90%), 3.12%, 01/20/31(a)(d)	USD		250	$	249,997
TICP CLO V Ltd., Series 2016-5A, Class ER, (3 mo. LIBOR US + 5.75%), 5.97%, 07/17/31(a)(d)			1,000		968,789
TICP CLO VI Ltd.
Series 2016-6A, Class AR2, (3 mo. LIBOR US + 1.12%), 1.26%, 01/15/34(a)(d)			4,870		4,851,195
Series 2016-6A, Class BR2, (3 mo. LIBOR US + 1.50%), 1.64%, 01/15/34(a)(d)			6,270		6,255,484
TICP CLO VII Ltd., Series 2017-7A, Class ER, (3 mo. LIBOR US + 7.05%), 7.29%, 04/15/33(a)(d)			750		753,402
TICP CLO XI Ltd., Series 2018-11A, Class A, (3 mo. LIBOR US + 1.18%), 1.40%, 10/20/31(a)(d)			750		750,213
TICP CLO XII Ltd., Series 2018-12A, Class A, (3 mo. LIBOR US + 1.11%), 1.35%, 01/15/31(a)(d)			250		250,209
Towd Point Mortgage Trust, Series 2019-SJ2, Class M1, 4.50%, 11/25/58(a)(d)			8,260		8,435,555
TRESTLES CLO III Ltd.
Series 2020-3A, Class A1, (3 mo. LIBOR US + 1.33%), 1.55%, 01/20/33(a)(d)			8,860		8,877,038
Series 2020-3A, Class B1, (3 mo. LIBOR US + 1.85%), 2.07%, 01/20/33(a)(d)			2,590		2,599,907
TRESTLES CLO Ltd.
Series 2017-1A, Class A1R, (3 mo. LIBOR US + 0.99%), 1.19%, 04/25/32(a)(d)			250		250,000
Series 2017-1A, Class CR, (3 mo. LIBOR US + 2.90%), 0.00%, 04/25/32(a)(d)			250		250,000
Tricon American Homes, Series 2020-SFR1, Class D, 2.55%, 07/17/38(a)			6,675		6,667,483
Tricon American Homes Trust
Series 2017-SFR1, Class D, 3.41%, 09/17/34(a)			2,784		2,807,418
Series 2017-SFR1, Class F, 5.15%, 09/17/34(a)			14,485		14,740,278
Series 2017-SFR2, Class F, 5.10%, 01/17/36(a)			8,715		9,017,024
Series 2018-SFR1, Class E, 4.56%, 05/17/37(a)			890		926,356
Series 2018-SFR1, Class F, 4.96%, 05/17/37(a)			610		638,165
Trimaran Cavu Ltd.
Series 2019-1A, Class B, (3 mo. LIBOR US + 2.20%), 2.42%, 07/20/32(a)(d)			750		755,195
Series 2019-1A, Class C1, (3 mo. LIBOR US + 3.15%), 3.37%, 07/20/32(a)(d)			500		501,692
Series 2019-1A, Class D, (3 mo. LIBOR US + 4.15%), 4.37%, 07/20/32(a)(d)			500		503,224
Trimaran CAVU Ltd., Series 2019-2A, Class C, (3 mo. LIBOR US + 4.72%), 4.94%, 11/26/32(a)(d)			500		501,389
Trinitas CLO XI Ltd., Series 2019-11A, Class C, (3 mo. LIBOR US + 3.15%), 3.39%, 07/15/32(a)(d)			2,177		2,183,750
Trinitas CLO XIV Ltd.
Series 2020-14A, Class B, (3 mo. LIBOR US + 2.00%), 2.24%, 01/25/34(a)(d)			3,460		3,467,854

40 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Asset-Backed Securities (continued)
Trinitas CLO XIV Ltd.
Series 2020-14A, Class C, (3 mo. LIBOR US + 3.00%), 3.24%, 01/25/34(a)(d)	USD		2,290	$	2,301,193
VCAT LLC, Series 2020-NPL1, Class A1, 3.67%, 08/25/50(a)(c)			6,310		6,373,441
Venture CLO Ltd.
Series 2018-32A, Class A2A, (3 mo. LIBOR US + 1.07%), 1.29%, 07/18/31(a)(d)			1,480		1,476,389
Series 2018-35A, Class AS, (3 mo. LIBOR US + 1.65%), 1.87%, 10/22/31(a)(d)			2,810		2,810,489
Venture XVI CLO Ltd., Series 2014-16A, Class BRR, 1.49%, 01/15/28(a)(d)			300		298,200
Venture XVIII CLO Ltd., Series 2014-18A, Class AR, (3 mo. LIBOR US + 1.22%), 1.46%, 10/15/29(a)(d)			9,820		9,821,753
Vibrant CLO VII Ltd., Series 2017-7A, Class A1, (3 mo. LIBOR US + 1.27%), 1.49%, 09/15/30(a)(d)			1,750		1,748,522
Voya CLO Ltd.
Series 2014-3A, Class CR, (3 mo. LIBOR US + 2.65%), 2.87%, 07/25/26(a)(d)			1,680		1,679,874
Series 2014-4A, Class A1RA, (3 mo. LIBOR US + 1.10%), 1.33%, 07/14/31(a)(d)			248		247,414
Series 2015-2A, Class BR, (3 mo. LIBOR US + 1.50%), 1.72%, 07/23/27(a)(d)			780		772,665
Series 2017-3A, Class A1A, (3 mo. LIBOR US + 1.23%), 1.45%, 07/20/30(a)(d)			2,201		2,201,547
Series 2017-3A, Class A1R, (3 mo. LIBOR US + 1.04%), 1.24%, 04/20/34(a)(b)(d)			2,178		2,178,000
Series 2017-4A, Class A1, (3 mo. LIBOR US + 1.13%), 1.37%, 10/15/30(a)(d)			6,640		6,642,886
Series 2019-1A, Class AR, (3 mo. LIBOR US + 1.06%), 1.30%, 04/15/31(a)(d)			10,079		10,109,102
Voya Euro CLO II DAC, Series 2X, Class C, (3 mo. EURIBOR + 2.75%), 2.75%, 07/15/32(d)	EUR		730		852,799
Wachovia Asset Securitization Issuance II LLC Trust, Series 2007-HE2A, Class A, (1 mo. LIBOR US + 0.13%), 0.25%, 07/25/37(a)(d)	USD		1,311		1,202,905
Washington Mutual Asset-Backed Certificates Trust
Series 2006-HE4, Class 2A2, (1 mo. LIBOR US + 0.18%), 0.29%, 09/25/36(d)			4,817		2,149,659
Series 2006-HE5, Class 1A, (1 mo. LIBOR US + 0.16%), 0.26%, 10/25/36(d)			1,750		1,504,813
Series 2007-HE3, Class 2A3, (1 mo. LIBOR US + 0.24%), 0.35%, 05/25/37(d)			1,223		1,108,486
Wellfleet CLO Ltd., Series 2017-3A, Class B, (3 mo. LIBOR US + 1.95%), 2.17%, 01/17/31(a)(d)			750		746,748
Westcott Park CLO Ltd., Series 2016-1A, Class AR, (3 mo. LIBOR US + 1.21%), 1.43%, 07/20/28(a)(d)			5,610		5,610,580
Whitebox CLO I Ltd.
Series 2019-1A, Class C, (3 mo. LIBOR US + 4.35%), 4.57%, 07/24/32(a)(d)			2,570		2,575,903
Series 2019-1A, Class D, (3 mo. LIBOR US + 7.45%), 7.67%, 07/24/32(a)(d)			2,000		1,999,596
Whitebox CLO II Ltd.
Series 2020-2A, Class A1, (3 mo. LIBOR US + 1.75%), 1.99%, 10/24/31(a)(d)			1,470		1,472,835

Security		Par (000)		Value
Asset-Backed Securities (continued)
Whitebox CLO II Ltd.
Series 2020-2A, Class B, (3 mo. LIBOR US + 2.25%), 2.49%, 10/24/31(a)(d)	USD		1,470	$	1,475,712
Series 2020-2A, Class D, (3 mo. LIBOR US + 4.15%), 4.39%, 10/24/31(a)(d)			1,470		1,474,189
Woodmont Trust, Series 2017-2A, Class A1R, (3 mo. LIBOR US + 1.67%), 0.00%, 04/20/33(a)(d)			9,340		9,315,659
Yale Mortgage Loan Trust, Series 2007-1, Class A, (1 mo. LIBOR US + 0.40%), 0.51%, 06/25/37(a)(d)			2,354		1,017,446
York CLO 1 Ltd.
Series 2014-1A, Class BRR, (3 mo. LIBOR US + 1.65%), 1.87%, 10/22/29(a)(d)			750		751,113
Series 2014-1A, Class DRR, (3 mo. LIBOR US + 3.01%), 3.23%, 10/22/29(a)(d)			250		247,554
York CLO-2 Ltd., Series 2015-1A, Class AR, (3 mo. LIBOR US + 1.15%), 1.37%, 01/22/31(a)(d)			250		250,116
York CLO-3 Ltd., Series 2016-1A, Class BR, (3 mo. LIBOR US + 1.75%), 1.97%, 10/20/29(a)(d)			3,380		3,384,194
York CLO-4 Ltd.
Series 2016-2A, Class A1R, (3 mo. LIBOR US + 1.09%), 1.31%, 04/20/32(a)(d)			8,250		8,247,565
Series 2016-2A, Class BR, (3 mo. LIBOR US + 1.55%), 1.77%, 04/20/32(a)(d)			3,000		2,983,771
Series 2016-2A, Class CR, (3 mo. LIBOR US + 2.15%), 2.37%, 04/20/32(a)(d)			3,000		2,973,642
York CLO-7 Ltd., Series 2019-2A, Class C, (3 mo. LIBOR US + 2.75%), 2.97%, 01/22/33(a)(d)			500		498,854
York CLO-8 Ltd., Series 2020-1A, Class E, (3 mo. LIBOR US + 7.88%), 8.05%, 04/20/32(a)(d)			500		502,341
Total Asset-Backed Securities — 11.3% (Cost: $2,363,226,773)					2,368,991,688
		Shares
Common Stocks
Capital Markets — 0.1%
UWM Holdings Corp. (Acquired 01/20/21, cost $12,898,845)(e)(f)			1,438,855		11,410,120
Diversified Financial Services — 0.2%
ArcLight Clean Transition Corp. II(g)			133,021		1,330,210
Climate Real Impact Solutions II Acquisition Corp.(g)			55,285		552,850
Crown PropTech Acquisitions(g)			385,188		3,828,769
Crown PropTech Acquisitions(b)			147,660		642
dMY Technology Group, Inc. II(g)(h)			50,556		743,679
Jaws Mustang Acquisition Corp.(g)			350,934		3,561,980
KINS Technology Group, Inc.(g)			798,484		8,080,658
KINS Technology Group, Inc.(b)			249,500		189,620
Liberty Media Acquisition Corp.(g)			71,525		766,033
Northern Genesis Acquisition Corp. II(g)			54,160		554,598
Pivotal Investment Corp. III(g)			155,262		1,552,620
Queen’s Gambit Growth Capital(g)			213,014		2,145,051
Reinvent Technology Partners Y(g)			200,096		2,008,964
Rotor Acquisition Corp.(g)			268,519		2,687,875
Rotor Acquisition Corp.(b)			74,080		81,867

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 41

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Shares		Value
Diversified Financial Services (continued)
Science Strategic Acquisition Corp. Alpha(g)			167,395	$	1,663,906
Thimble Point Acquisition Corp.(g)			191,496		1,914,960
Thoma Bravo Advantage, Class A(g)			140,000		1,463,000
Tishman Speyer Innovation Corp. II(g)			99,570		997,691
					34,124,973
Energy Equipment & Services — 0.0%
Pioneer Energy Services Corp.(b)(h)			7,278		42,212
Vantage Drilling Co.(g)			311,000		1,882
					44,094
Equity Real Estate Investment Trusts (REITs) — 0.1%
DiamondRock Hospitality Co.(g)			560,822		5,776,467
Park Hotels & Resorts, Inc.			264,483		5,707,543
Service Properties Trust			574,385		6,812,206
Sunstone Hotel Investors, Inc.			386,245		4,812,613
Xenia Hotels & Resorts, Inc.			309,157		6,028,561
					29,137,390
Health Care Providers & Services — 0.0%
HCA Healthcare, Inc.			5,916		1,114,219
Hotels, Restaurants & Leisure — 0.1%
Caesars Entertainment, Inc.(g)			297,200		25,990,140
Household Durables — 0.0%
Beazer Homes U.S.A., Inc.(g)			52,287		1,093,844
Century Communities, Inc.(e)(g)			56,406		3,402,410
Taylor Morrison Home Corp.(g)			202,363		6,234,804
					10,731,058
Internet & Direct Marketing Retail — 0.1%
Amazon.com, Inc.(e)(g)			4,660		14,418,413
IT Services — 0.0%
Sabre Corp.			5,000		74,050
Media — 0.0%
Altice USA, Inc., Class A(g)			77,054		2,506,567
Metals & Mining — 0.0%
Northern Graphite Corp.(g)			99,612		30,517
Oil, Gas & Consumable Fuels — 0.1%
California Resources Corp.(g)			485,564		11,682,670
California Resources Corp.(g)			145,873		3,483,381
Chesapeake Energy Corp.(g)			347		15,056
Chesapeake Energy Corp. (Acquired 02/09/21, cost $50,485)(f)			5,331		222,836
Diamondback Energy, Inc.			8,636		634,660
Green Plains, Inc.(g)			229,469		6,211,726
					22,250,329
Real Estate Management & Development — 0.1%
Forestar Group, Inc.(g)			128,970		3,002,422
Opendoor Technologies, Inc.(g)(h)			833,000		17,651,270
					20,653,692
Total Common Stocks — 0.8% (Cost: $145,561,463)					172,485,562
		Par (000)
Corporate Bonds
Aerospace & Defense — 1.4%
BAE Systems Holdings, Inc., 3.85%, 12/15/25(a)	USD		10,484		11,540,809
BAE Systems PLC, 3.40%, 04/15/30(a)			15,747		16,714,811

Security		Par (000)		Value
Aerospace & Defense (continued)
Boeing Co.
2.80%, 03/01/23	USD		2,463	$	2,552,358
2.85%, 10/30/24			2,714		2,840,050
5.93%, 05/01/60			3,561		4,569,209
Bombardier, Inc.
8.75%, 12/01/21(a)			2,000		2,098,340
5.75%, 03/15/22(a)			1,000		1,042,500
6.00%, 10/15/22(a)			525		525,000
6.13%, 01/15/23(a)			188		195,755
Embraer Netherlands Finance BV
5.40%, 02/01/27			947		987,177
6.95%, 01/17/28(a)			1,227		1,343,933
Embraer Overseas Ltd., 5.70%, 09/16/23			1,337		1,403,432
General Dynamics Corp. 3.75%, 05/15/28			4,050		4,513,034
3.63%, 04/01/30			11,208		12,389,644
Huntington Ingalls Industries, Inc. 3.84%, 05/01/25			5,245		5,722,591
4.20%, 05/01/30			7,846		8,703,402
L3Harris Technologies, Inc. 3.85%, 12/15/26			8,165		9,039,810
4.40%, 06/15/28			13,382		15,185,142
4.40%, 06/15/28			3,547		4,024,936
2.90%, 12/15/29			2,864		2,950,555
1.80%, 01/15/31			13,168		12,333,265
Lockheed Martin Corp. 3.60%, 03/01/35			14,240		15,863,369
3.80%, 03/01/45			1,981		2,179,643
2.80%, 06/15/50			4,958		4,676,127
Northrop Grumman Corp. 3.25%, 01/15/28			21,091		22,625,158
4.03%, 10/15/47			3,320		3,692,312
5.25%, 05/01/50			4,905		6,356,437
Raytheon Technologies Corp. 3.15%, 12/15/24			4,040		4,341,932
7.20%, 08/15/27			2,353		3,080,064
7.00%, 11/01/28			7,205		9,266,300
4.13%, 11/16/28			16,841		18,965,214
7.50%, 09/15/29			475		654,050
2.15%, 05/18/30	EUR		4,391		5,781,272
2.25%, 07/01/30	USD		13,010		12,803,796
4.50%, 06/01/42			4,200		5,008,481
4.15%, 05/15/45			3,755		4,147,888
4.63%, 11/16/48			2,553		3,054,464
Textron, Inc. 3.90%, 09/17/29			8,086		8,752,248
2.45%, 03/15/31			2,258		2,186,672
TransDigm, Inc. 8.00%, 12/15/25(a)			9,810		10,683,090
6.25%, 03/15/26(a)			23,463		24,875,473
United Technologies Corp., 5.40%, 05/01/35			863		1,091,049
					290,760,792
Air Freight & Logistics — 0.2%
FedEx Corp. 3.88%, 08/01/42			2,943		3,109,465
4.55%, 04/01/46			1,320		1,495,594
GLP China Holdings Ltd., 2.95%, 03/29/26			1,320		1,314,134
United Parcel Service, Inc. 3.40%, 03/15/29			7,874		8,559,152
2.50%, 09/01/29			4,016		4,093,664
4.45%, 04/01/30			11,440		13,371,082
5.20%, 04/01/40			9,890		12,703,801

42 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Air Freight & Logistics (continued)
XPO Logistics, Inc. 6.13%, 09/01/23(a)	USD		1,462	$	1,487,556
6.75%, 08/15/24(a)			3,480		3,649,650
					49,784,098
Airlines — 0.7%
Air Canada Pass-Through Trust
Series 2017-1, Class AA, 3.30%, 01/15/30(a)			1,918		1,867,934
Series 2017-1, Class B, 3.70%, 01/15/26(a)			19		18,086
Allegiant Travel Co., 8.50%, 02/05/24(a)			5,339		5,766,120
American Airlines Pass-Through Trust 4.95%, 01/15/23			2,621		2,620,378
4.00%, 12/15/25(b)			1,555		1,523,557
3.50%, 12/15/27(b)			4,525		4,457,482
Series 2015-2, Class AA, 3.60%, 09/22/27			1,003		1,009,644
Series 2015-2, Class B, 4.40%, 09/22/23			5,317		5,023,333
Series 2016-1, Class AA, 3.58%, 01/15/28			4,003		4,052,633
Series 2016-1, Class B, 5.25%, 01/15/24			4,073		3,865,656
Series 2016-2, Class AA, 3.20%, 06/15/28			1,841		1,833,224
Series 2016-3, Class AA, 3.00%, 10/15/28			11,023		11,110,927
Series 2016-3, Class B, 3.75%, 10/15/25			70		65,714
Series 2017-1, Class AA, 3.65%, 02/15/29			1,407		1,418,259
Series 2017-1, Class B, 4.95%, 02/15/25			1,216		1,131,949
Series 2019-1, Class AA, 3.15%, 02/15/32			4,994		4,970,513
Series 2019-1, Class B, 3.85%, 02/15/28			5,162		4,692,398
American Airlines, Inc. 4.13%, 06/15/22(b)			15,927		15,509,713
4.87%, 10/22/23(b)			949		923,184
Avianca Holdings SA
(3 mo. LIBOR US + 10.50% (Cash), 3 mo. LIBOR US + 12.00% (PIK)), 12.20%, 11/10/21(a)(i)			2,417		2,440,257
(3 mo. LIBOR US + 10.50% (Cash), 3 mo. LIBOR US + 12.00% (PIK)), 12.20%, 11/10/21(a)(i)			170		171,811
British Airways Pass-Through Trust
Series 2020-1, Class A, 4.25%, 11/15/32(a)			2,085		2,184,219
Series 2020-1, Class B, 8.38%, 11/15/28(a)			1,645		1,872,084
Delta Air Lines Pass-Through Trust, Series 2019-1, Class AA, 3.20%, 04/25/24			12,694		13,149,538
GOL Equity Finance SA, 3.75%, 07/15/24(a)(j)			790		650,450
Gol Finance, Inc., 7.00%, 01/31/25(a)			4,700		3,827,563
Singapore Airlines Ltd., 1.63%, 12/03/25(j)	SGD		750		672,112
Sun Country Airlines
Series 2019-1B, 4.70%, 12/15/25(b)	USD		2,165		2,075,518
Series 2019-1C, 7.00%, 12/15/25(b)			2,170		2,088,265
Transportes Aereos Portugueses SA, 5.63%, 12/02/24(a)	EUR		400		362,808
Turkish Airlines Pass-Through Trust, Series 2015-1, Class A, 4.20%, 03/15/27(a)	USD		1,285		1,155,216
United Airlines Pass-Through Trust
Series 2014-1, Class A, 4.00%, 04/11/26			3,692		3,819,584
Series 2014-1, Class B, 4.75%, 04/11/22			334		339,509
Series 2014-2, Class B, 4.63%, 09/03/22			381		389,252
Series 2015-1, Class AA, 3.45%, 12/01/27			1,428		1,492,688
Series 2016-1, Class AA, 3.10%, 07/07/28			558		570,948
Series 2016-2, Class AA, 2.88%, 10/07/28			1,756		1,782,450
Series 2016-2, Class B, 3.65%, 10/07/25			227		222,297
Series 2018-1, Class AA, 3.50%, 03/01/30			1,184		1,211,405
Series 2019-2, Class AA, 2.70%, 05/01/32			3,315		3,219,906
Series 2019-2, Class B, 3.50%, 05/01/28			4,728		4,601,126

Security		Par (000)		Value
Airlines (continued)
United Airlines Pass-Through Trust
Series 2020-1, Class A, 5.88%, 10/15/27	USD		24,473	$	27,132,735
Series 2020-1, Class B, 4.88%, 01/15/26			3,870		4,015,125
					151,307,570
Auto Components — 0.0%
American Axle & Manufacturing, Inc., 6.25%, 04/01/25			1,860		1,915,800
Magna International, Inc., 2.45%, 06/15/30			4,046		4,070,916
					5,986,716
Automobiles — 0.4%
BMW U.S. Capital LLC, 2.55%, 04/01/31(a)			4,699		4,711,773
Daimler Finance North America LLC, 3.35%, 05/04/21(a)			13,164		13,195,815
General Motors Co., 6.13%, 10/01/25			6,381		7,503,471
Nissan Motor Acceptance Corp., 2.75%, 03/09/28(a)			3,493		3,464,584
Nissan Motor Co. Ltd. 3.52%, 09/17/25(a)			10,201		10,806,238
4.81%, 09/17/30(a)			30,836		33,820,501
					73,502,382
Banks — 6.0%
Arab National Bank, 3.33%, 10/28/30			775		791,227
Banco Espirito Santo SA 2.63%, 05/08/17(g)(k)	EUR		400		65,671
4.75%, 01/15/18(g)(k)			2,200		361,192
4.00%, 01/21/19(g)(k)			6,300		1,034,321
Banco Santander SA 2.71%, 06/27/24	USD		17,000		17,937,648
1.85%, 03/25/26			10,200		10,180,459
3.31%, 06/27/29			4,400		4,663,533
Banco Votorantim SA, 4.00%, 09/24/22(a)			1,258		1,298,492
Bangkok Bank PCL, 3.73%, 09/25/34			1,445		1,454,934
Bank of America Corp. 3.50%, 05/17/22			10,605		10,644,517
2.82%, 07/21/23			2,979		3,066,727
3.00%, 12/20/23			3,584		3,727,521
3.55%, 03/05/24			6,568		6,929,728
4.20%, 08/26/24			2,061		2,273,191
0.81%, 10/24/24			4,095		4,105,149
4.00%, 01/22/25			6,239		6,832,391
2.46%, 10/22/25			57,084		59,834,878
3.37%, 01/23/26			7,675		8,262,786
2.02%, 02/13/26			27		27,655
4.45%, 03/03/26			11,549		12,981,271
1.20%, 10/24/26			12,133		11,975,731
3.56%, 04/23/27			21,838		23,763,517
3.82%, 01/20/28			28,575		31,392,837
3.71%, 04/24/28			15,339		16,777,722
3.59%, 07/21/28			4,479		4,861,057
3.42%, 12/20/28			31,383		33,701,580
3.97%, 03/05/29			15,446		17,019,414
4.27%, 07/23/29			12,156		13,667,079
3.97%, 02/07/30			12,139		13,472,901
3.19%, 07/23/30			4,932		5,177,260
2.59%, 04/29/31			2,136		2,131,541
1.92%, 10/24/31			14,287		13,445,005
2.68%, 06/19/41			13,366		12,513,009
Series L, 3.95%, 04/21/25			6,388		7,004,174
Bank of East Asia Ltd., 4.00%, 05/29/30			2,160		2,249,100
Bank Tabungan Negara Persero Tbk PT, 4.20%, 01/23/25			200		203,063

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 43

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Banks (continued)
Barclays PLC 4.97%, 05/16/29	USD		18,105	$	20,817,864
2.67%, 03/10/32			6,874		6,709,983
3.81%, 03/10/42			6,862		6,722,272
BNP Paribas SA 3.38%, 01/09/25(a)			1,931		2,072,849
4.38%, 09/28/25(a)			2,732		3,024,399
2.82%, 11/19/25(a)			19,533		20,561,537
3.05%, 01/13/31(a)			14,562		14,927,300
BPCE SA, 2.70%, 10/01/29(a)			13,404		13,592,377
Citigroup, Inc. 4.40%, 06/10/25			10,647		11,831,184
4.60%, 03/09/26			1,933		2,181,170
3.20%, 10/21/26			3,890		4,180,109
3.67%, 07/24/28			34,845		38,107,288
4.08%, 04/23/29			10,845		12,065,066
3.98%, 03/20/30			6,129		6,785,133
2.98%, 11/05/30			49,919		51,625,619
2.67%, 01/29/31			3,834		3,852,120
Citizens Financial Group, Inc., 3.25%, 04/30/30			2,910		3,089,971
Danske Bank A/S 5.00%, 01/12/22(a)			13,526		13,979,663
3.00%, 09/20/22(a)			927		936,321
1.17%, 12/08/23(a)			3,435		3,453,781
5.38%, 01/12/24(a)			14,017		15,630,220
1.62%, 09/11/26(a)			3,505		3,467,101
Grupo Aval Ltd., 4.75%, 09/26/22			1,073		1,118,603
HSBC Holdings PLC 4.29%, 09/12/26			1,949		2,157,237
4.58%, 06/19/29			12,056		13,548,502
3.97%, 05/22/30			14,619		15,819,298
Huntington National Bank, 3.25%, 05/14/21			3,780		3,782,781
ING Groep NV 4.10%, 10/02/23			23,473		25,412,213
4.63%, 01/06/26(a)			18,232		20,666,018
1.73%, 04/01/27			4,514		4,516,608
Intesa Sanpaolo SpA, 3.13%, 07/14/22(a)			2,686		2,761,336
Itau Unibanco Holding SA 2.90%, 01/24/23(a)			4,491		4,580,820
3.25%, 01/24/25(a)			2,456		2,503,278
JPMorgan Chase & Co. 0.65%, 09/16/24			10,490		10,510,400
4.02%, 12/05/24			26,903		29,187,652
3.22%, 03/01/25			16,439		17,538,417
3.90%, 07/15/25			11,317		12,492,710
2.30%, 10/15/25			29,327		30,527,523
2.01%, 03/13/26			24,013		24,693,770
2.08%, 04/22/26			22,177		22,777,210
3.20%, 06/15/26			200		216,208
2.95%, 10/01/26			3,797		4,061,340
1.05%, 11/19/26			3,141		3,067,835
3.96%, 01/29/27			9,112		10,077,480
3.78%, 02/01/28			31,394		34,601,901
3.54%, 05/01/28			31,691		34,490,893
2.18%, 06/01/28			2,018		2,039,029
3.51%, 01/23/29			1,555		1,681,454
4.01%, 04/23/29			5,030		5,609,356
4.45%, 12/05/29			15,773		18,067,373
4.26%, 02/22/48			6,469		7,510,861
4.03%, 07/24/48			7,638		8,562,310
3.90%, 01/23/49			4,253		4,680,152
Kasikornbank PCL, 3.34%, 10/02/31			1,708		1,741,626

Security		Par (000)		Value
Banks (continued)
KeyCorp 4.10%, 04/30/28	USD		718	$	809,462
2.55%, 10/01/29			3,481		3,524,191
Lloyds Banking Group PLC 3.75%, 01/11/27			4,263		4,675,463
1.63%, 05/11/27			9,994		9,921,346
3.57%, 11/07/28			11,450		12,364,018
Mitsubishi UFJ Financial Group, Inc. 3.00%, 02/22/22			3,776		3,863,689
2.62%, 07/18/22			206		211,687
3.46%, 03/02/23			13,006		13,713,806
0.85%, 09/15/24			10,565		10,575,726
2.19%, 02/25/25			17,155		17,695,369
1.41%, 07/17/25			4,615		4,611,833
Mizuho Financial Group, Inc. 2.63%, 04/12/21(a)			7,490		7,493,408
2.84%, 07/16/25			797		841,439
2.56%, 09/13/25			18,319		19,160,613
2.20%, 07/10/31			5,172		4,993,197
1.98%, 09/08/31			9,815		9,256,944
Santander UK Group Holdings PLC 2.88%, 08/05/21			12,877		12,984,666
1.09%, 03/15/25			5,520		5,524,471
1.53%, 08/21/26			8,185		8,116,745
3.82%, 11/03/28			2,393		2,612,730
Shizuoka Bank Ltd., (3 mo. LIBOR US - 0.50%), 0.00%, 01/25/23(d)(j)			200		196,100
Standard Chartered PLC, 3.89%, 03/15/24(a)			2,885		3,046,352
Sumitomo Mitsui Financial Group, Inc. 2.70%, 07/16/24			16,297		17,229,697
2.35%, 01/15/25			16,561		17,189,631
U.S. Bancorp, 3.00%, 07/30/29			3,250		3,405,617
Washington Mutual Escrow Bonds 0.00%(b)(g)(k)(l)			13,308		1
0.00%(b)(g)(k)(l)			11,911		1
0.00%(b)(g)(k)(l)			2,570		—
0.00%(b)(g)(k)(l)			3,115		—
Wells Fargo & Co. 3.00%, 04/22/26			9,290		9,927,412
3.20%, 06/17/27			2,599		2,785,669
3.58%, 05/22/28			9,767		10,648,624
2.39%, 06/02/28			2,086		2,137,929
2.88%, 10/30/30			9,441		9,725,284
3.07%, 04/30/41			26,271		25,761,523
					1,261,448,445
Beverages — 0.7%
Anheuser-Busch Cos. LLC/Anheuser-Busch InBev Worldwide, Inc., 4.70%, 02/01/36			32,375		37,926,293
Anheuser-Busch InBev Worldwide, Inc. 4.75%, 01/23/29			34,349		40,138,462
3.50%, 06/01/30			27,900		30,214,477
4.90%, 01/23/31			7,707		9,216,621
8.00%, 11/15/39			1,382		2,180,866
Central American Bottling Corp., 5.75%, 01/31/27(a)			1,707		1,807,286
Coca-Cola Co. 2.50%, 06/01/40			4,379		4,115,266
1.00%, 03/09/41	EUR		4,730		5,417,063
Keurig Dr Pepper, Inc., 3.20%, 05/01/30	USD		11,556		12,227,709

44 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Beverages (continued)
PepsiCo, Inc. 4.60%, 07/17/45	USD		1,586	$	1,945,882
3.38%, 07/29/49			2,819		2,911,947
					148,101,872
Biotechnology — 0.9%
AbbVie, Inc. 2.30%, 11/21/22			6,787		6,983,797
2.60%, 11/21/24(e)			27,141		28,655,422
3.80%, 03/15/25			13,744		15,015,864
3.60%, 05/14/25			18,485		20,138,042
3.20%, 05/14/26			16,440		17,760,387
4.55%, 03/15/35			12,142		14,100,270
4.50%, 05/14/35			9,578		11,246,316
4.45%, 05/14/46			2,398		2,762,900
4.88%, 11/14/48			7,823		9,422,094
Amgen, Inc. 2.45%, 02/21/30			10,152		10,222,312
4.40%, 05/01/45			12,437		14,398,893
Biogen, Inc. 2.25%, 05/01/30			10,692		10,372,395
3.15%, 05/01/50			4,587		4,212,515
Elanco Animal Health, Inc. 4.91%, 08/27/21			212		213,855
5.27%, 08/28/23			3,230		3,476,288
5.90%, 08/28/28			437		495,449
Gilead Sciences, Inc. 4.80%, 04/01/44			8,324		10,007,213
4.50%, 02/01/45			3,278		3,807,256
4.75%, 03/01/46			6,440		7,784,100
					191,075,368
Building Products — 0.0%
Johnson Controls International plc, 5.13%, 09/14/45			7		8,707
Masonite International Corp. 5.75%, 09/15/26(a)			120		124,800
5.38%, 02/01/28(a)			1,697		1,800,941
Owens Corning, 3.95%, 08/15/29			1,900		2,090,887
Standard Industries, Inc. 5.00%, 02/15/27(a)			1,674		1,745,145
4.75%, 01/15/28(a)			597		618,850
					6,389,330
Capital Markets — 2.3%
Bank of New York Mellon Corp., 3.44%, 02/07/28			6,475		7,115,928
CCTI 2017 Ltd., 3.63%, 08/08/22			1,675		1,696,461
Charles Schwab Corp., 3.20%, 03/02/27			3,391		3,685,121
Cindai Capital Ltd., 0.00%, 02/08/23(j)(m)			2,461		2,496,793
Credit Suisse AG, 3.63%, 09/09/24			6,918		7,497,002
Credit Suisse Group AG 3.80%, 06/09/23			3,341		3,545,069
3.00%, 12/14/23(a)			253		261,551
4.21%, 06/12/24(a)			3,162		3,377,022
Credit Suisse Group Funding Guernsey Ltd., 3.80%, 09/15/22			7,054		7,346,994
Deutsche Bank AG 1.45%, 04/01/25			21,847		21,839,395
1.69%, 03/19/26			15,536		15,501,485
3.55%, 09/18/31			3,813		3,937,254
Goldman Sachs Group, Inc. 3.50%, 01/23/25			20,740		22,381,576
3.50%, 04/01/25			50,076		54,252,970

Security		Par (000)		Value
Capital Markets (continued)
Goldman Sachs Group, Inc. 3.75%, 05/22/25	USD		2,180	$	2,379,785
3.27%, 09/29/25			11,495		12,334,938
(3 mo. LIBOR US + 1.17%), 1.36%, 05/15/26(d)			10,315		10,449,704
3.50%, 11/16/26			10,964		11,883,356
3.85%, 01/26/27			5,678		6,228,542
1.43%, 03/09/27			15,000		14,865,692
3.69%, 06/05/28			18,181		19,892,974
Intercontinental Exchange, Inc. 3.75%, 09/21/28			5,126		5,637,216
2.10%, 06/15/30			2,412		2,316,403
1.85%, 09/15/32			8,838		8,090,561
Lehman Brothers Holdings, Inc., 6.75%, 12/28/17(b)(g)(k)			7,360		1
Moody’s Corp., 3.25%, 01/15/28			4,450		4,778,906
Morgan Stanley 2.72%, 07/22/25			6,457		6,811,611
4.00%, 07/23/25			8,426		9,350,798
2.19%, 04/28/26			8,049		8,316,486
3.13%, 07/27/26			6,411		6,900,031
3.63%, 01/20/27			26,003		28,531,819
3.59%, 07/22/28			4,119		4,490,475
3.77%, 01/24/29			13,563		14,834,398
4.43%, 01/23/30			28,886		33,074,770
2.70%, 01/22/31			20,646		21,007,892
3.62%, 04/01/31			15,864		17,224,250
7.25%, 04/01/32			1,954		2,746,350
1.93%, 04/28/32			2,144		2,025,448
Northern Trust Corp., 3.15%, 05/03/29			3,064		3,283,668
State Street Corp., 2.40%, 01/24/30			5,108		5,196,753
UBS Group AG 2.86%, 08/15/23(a)			18,674		19,251,687
4.13%, 09/24/25(a)			22,600		25,084,959
4.13%, 04/15/26(a)			4,551		5,078,308
1.36%, 01/30/27(a)			8,756		8,628,555
					475,630,957
Chemicals — 0.4%
Braskem Netherlands Finance BV 4.50%, 01/10/28			1,420		1,458,411
5.88%, 01/31/50(a)			2,848		2,853,767
8.50%, 01/23/81(a)			2,808		3,187,080
8.50%, 01/23/81			993		1,127,055
Cydsa SAB de CV, 6.25%, 10/04/27(a)			3,902		4,087,345
Dow Chemical Co. 9.00%, 04/01/21			3,960		3,960,000
4.55%, 11/30/25			6,407		7,268,711
2.10%, 11/15/30			14,014		13,508,144
1.13%, 03/15/32	EUR		4,983		5,943,489
DuPont de Nemours, Inc., 4.49%, 11/15/25	USD		15,078		17,040,455
Ecolab, Inc. 4.80%, 03/24/30			3,346		4,002,566
1.30%, 01/30/31			559		513,521
GC Treasury Center Co. Ltd., 2.98%, 03/18/31			545		538,820
LYB International Finance III LLC, 4.20%, 05/01/50			7,049		7,577,905
Mitsubishi Chemical Holdings Corp. 0.00%, 03/30/22(j)(m)	JPY		150,000		1,356,740
0.00%, 03/29/24(j)(m)			40,000		374,441
RPM International, Inc., 4.25%, 01/15/48	USD		155		157,800
Sasol Financing U.S.A. LLC 5.88%, 03/27/24			1,461		1,543,145

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 45

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Chemicals (continued)
Sasol Financing U.S.A. LLC 4.38%, 09/18/26	USD		1,705	$	1,732,962
5.50%, 03/18/31			2,795		2,732,112
Sherwin-Williams Co. 4.20%, 01/15/22			2,800		2,856,774
2.95%, 08/15/29			886		922,693
2.30%, 05/15/30			8,672		8,540,813
					93,284,749
Commercial Services & Supplies — 0.2%
Beijing Environment Bvi Co. Ltd., 5.30%, 10/18/21			680		690,625
Clean Harbors, Inc., 4.88%, 07/15/27(a)			2,288		2,413,840
KAR Auction Services, Inc., 5.13%, 06/01/25(a)			2,696		2,744,663
Legends Hospitality Holding Co. LLC/Legends Hospitality Co-Issuer, Inc., 5.00%, 02/01/26(a)			350		356,125
Pitney Bowes, Inc. 6.88%, 03/15/27(a)			2,775		2,750,719
7.25%, 03/15/29(a)			1,750		1,730,592
Republic Services, Inc. 2.90%, 07/01/26			2,994		3,192,894
3.95%, 05/15/28			9,162		10,224,863
1.45%, 02/15/31			4,938		4,514,388
Waste Management, Inc., 1.15%, 03/15/28			10,160		9,624,744
Waste Pro USA, Inc., 5.50%, 02/15/26(a)			1,398		1,431,202
					39,674,655
Communications Equipment — 0.1%
CommScope Technologies LLC, 6.00%, 06/15/25(a)			2,000		2,040,100
CommScope, Inc., 8.25%, 03/01/27(a)			2,000		2,140,000
Juniper Networks, Inc., 2.00%, 12/10/30			4,462		4,106,031
Motorola Solutions, Inc. 4.60%, 05/23/29			10,242		11,617,570
5.50%, 09/01/44			6,050		7,335,070
					27,238,771
Construction & Engineering — 0.0%
China City Construction International Co. Ltd., 5.35%, 07/03/17(b)(g)(k)	CNH		340		—
GMR Hyderabad International Airport Ltd., 5.38%, 04/10/24	USD		400		411,000
					411,000
Construction Materials — 0.0%
Cemex SAB de CV 5.20%, 09/17/30(a)			2,229		2,401,747
3.88%, 07/11/31(a)			2,848		2,781,072
U.S. Concrete, Inc., 6.38%, 06/01/24			543		554,539
					5,737,358
Consumer Finance — 0.7%
Alpha Holding SA de CV, 9.00%, 02/10/25(a)			3,084		2,198,314
American Express Co., 3.70%, 08/03/23			6,764		7,239,743
Capital One Financial Corp. 4.75%, 07/15/21			546		552,753
3.90%, 01/29/24			11,689		12,637,895
Discover Bank, 3.45%, 07/27/26			2,008		2,173,003
Discover Financial Services, 4.50%, 01/30/26			4,031		4,545,177
General Motors Financial Co., Inc. 5.20%, 03/20/23			31,703		34,381,585
3.70%, 05/09/23			8,790		9,258,101
5.10%, 01/17/24			4,641		5,132,390
4.00%, 01/15/25			14,339		15,575,457

Security		Par (000)		Value
Consumer Finance (continued)
General Motors Financial Co., Inc. 4.35%, 04/09/25	USD		5,855	$	6,421,879
2.75%, 06/20/25			10,721		11,191,686
Hyundai Capital Services, Inc. 3.00%, 08/29/22(a)			7,790		8,024,401
1.25%, 02/08/26			715		697,654
Navient Corp. 6.63%, 07/26/21			1,857		1,891,819
6.50%, 06/15/22			2,529		2,652,592
7.25%, 09/25/23			1,473		1,594,277
5.88%, 10/25/24			1,377		1,446,001
6.75%, 06/25/25			1,446		1,569,994
6.75%, 06/15/26			1,424		1,543,616
Toyota Motor Credit Corp. 2.15%, 02/13/30			6,889		6,841,996
3.38%, 04/01/30			4,173		4,529,462
1.65%, 01/10/31			3,914		3,692,517
					145,792,312
Containers & Packaging — 0.1%
Ardagh Packaging Finance PLC/Ardagh Holdings USA, Inc. 4.13%, 08/15/26(a)			299		306,394
5.25%, 08/15/27(a)			2,217		2,261,517
Ball Corp. 5.25%, 07/01/25			597		674,610
4.88%, 03/15/26			448		501,003
International Paper Co. 6.00%, 11/15/41			2,411		3,270,353
4.40%, 08/15/47			2,477		2,898,496
Klabin Austria GmbH, 3.20%, 01/12/31(a)			2,015		1,914,250
Owens-Brockway Glass Container, Inc., 5.88%, 08/15/23(a)			2,010		2,153,213
					13,979,836
Diversified Consumer Services — 0.0%
Bright Scholar Education Holdings Ltd., 7.45%, 07/31/22			200		207,438
China Education Group Holdings Ltd., 2.00%, 03/28/24(j)	HKD		8,000		1,223,035
					1,430,473
Diversified Financial Services — 0.9%
AerCap Ireland Capital DAC/AerCap Global Aviation Trust 3.50%, 01/15/25	USD		575		602,966
1.75%, 01/30/26			2,198		2,134,839
4.45%, 04/03/26			5,250		5,683,942
3.65%, 07/21/27			217		227,704
ANLLIAN Capital Ltd., 0.00%, 02/05/25(j)(m)	EUR		800		1,212,906
ASG Finance Designated Activity Co., 7.88%, 12/03/24(a)	USD		4,118		3,849,043
Azul Investments LLP, 5.88%, 10/26/24(a)			1,759		1,540,550
Capitol Investment Merger Sub 2 LLC, 10.00%, 08/01/24(a)			4,232		4,574,792
China Huadian Overseas Development 2018 Ltd., 3.38%(l)			2,165		2,227,244
Coastal Emerald Ltd. 4.30%(l)			1,190		1,212,312
3.95%, 08/01/22			695		705,069
Deutsche Telekom International Finance BV, 3.60%, 01/19/27(a)			4,339		4,754,692
Easy Tactic Ltd. 9.13%, 07/28/22			200		199,313

46 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Diversified Financial Services (continued)
Easy Tactic Ltd.
8.63%, 02/27/24	USD		830	$	769,825
Fortune Star BVI Ltd.
5.95%, 01/29/23			200		204,625
6.85%, 07/02/24			540		569,531
5.95%, 10/19/25			695		726,275
5.05%, 01/27/27			200		200,560
GE Capital International Funding Co., 4.42%, 11/15/35			10,825		12,392,027
Glencore Funding LLC, 2.50%, 09/01/30(a)			12,744		12,255,070
Grupo Aval Ltd., 4.38%, 02/04/30(a)			5,009		5,038,741
Hyundai Capital America
3.95%, 02/01/22(a)			3,655		3,754,370
2.38%, 02/10/23(a)			15,891		16,293,241
InRetail Consumer, 3.25%, 03/22/28(a)			1,985		1,981,278
Intercorp Peru Ltd., 3.88%, 08/15/29(a)			372		381,998
Latam Finance Ltd., 6.88%, 04/11/24(g)(k)			873		720,225
Manappuram Finance Ltd., 5.90%, 01/13/23			400		413,625
Muthoot Finance Ltd., 4.40%, 09/02/23			200		202,875
Operadora de Servicios Mega SA de CV Sofom
ER, 8.25%, 02/11/25(a)			5,482		5,537,848
ORIX Corp., 2.90%, 07/18/22			4,137		4,262,534
Pacific National Finance Pty Ltd., 4.75%, 03/22/28			1,100		1,151,874
Pearl Holding III Ltd., 9.50%, 12/11/22			600		186,375
Prime Bloom Holdings Ltd., 6.95%, 07/05/22			890		168,822
Quicken Loans LLC/Quicken Loans Co-Issuer, Inc., 3.63%, 03/01/29(a)			3,343		3,217,637
Quicken Loans, Inc., 5.25%, 01/15/28(a)			3,322		3,488,100
RELX Capital, Inc.
3.50%, 03/16/23			6,730		7,088,631
4.00%, 03/18/29			11,279		12,441,349
3.00%, 05/22/30			15,042		15,600,803
Santos Finance Ltd., 5.25%, 03/13/29			1,500		1,641,941
Shell International Finance BV
3.88%, 11/13/28			7,369		8,225,562
2.38%, 11/07/29			13,627		13,751,707
2.75%, 04/06/30			9,628		9,943,282
4.38%, 05/11/45			2,800		3,277,645
Shriram Transport Finance Co. Ltd.
5.95%, 10/24/22			436		446,628
5.10%, 07/16/23			243		246,873
Simpar Europe SA, 5.20%, 01/26/31(a)			3,105		3,040,959
Trust Fibra Uno
5.25%, 01/30/26(a)			2,025		2,230,031
6.95%, 01/30/44(a)			2,194		2,545,726
6.39%, 01/15/50(a)			1,422		1,565,977
United Shore Financial Services LLC, 5.50%, 11/15/25(a)			9,586		9,993,405
					194,883,347
Diversified Telecommunication Services — 1.8%
AT&T Inc.
0.00%, 11/27/22(a)(m)			36,000		35,688,501
1.70%, 03/25/26			10,515		10,511,308
3.80%, 02/15/27			4,908		5,427,691
4.25%, 03/01/27			5,463		6,139,333
2.30%, 06/01/27			3,615		3,694,563
1.65%, 02/01/28			4,794		4,644,292
4.35%, 03/01/29			13,151		14,876,130
2.75%, 06/01/31			12,906		12,854,207
2.25%, 02/01/32			10,695		10,172,420
2.55%, 12/01/33(a)			4,155		3,944,719

Security		Par (000)		Value
Diversified Telecommunication Services (continued)
AT&T Inc.
4.50%, 05/15/35	USD		13,224	$	14,914,888
2.60%, 05/19/38	EUR		5,000		6,612,715
4.90%, 06/15/42	USD		2,043		2,384,145
4.55%, 03/09/49			2,194		2,410,717
3.50%, 09/15/53(a)			13,342		12,329,820
3.55%, 09/15/55(a)			10,340		9,462,201
3.80%, 12/01/57(a)			3,260		3,101,520
Avaya, Inc., 6.13%, 09/15/28(a)			3,000		3,184,695
Axtel SAB de CV, 6.38%, 11/14/24(a)			2,516		2,626,861
Bharti Airtel International Netherlands BV, 5.35%, 05/20/24			922		1,015,666
Connect Finco S.a.r.l/Connect U.S. Finco LLC, 6.75%, 10/01/26(a)			5,764		6,137,161
Digicel International Finance Ltd./Digicel Holdings Bermuda Ltd. 8.75%, 05/25/24(a)			1,109		1,139,127
(6.00% Cash and 7.00% PIK), 13.00%, 12/31/25(a)(i)			588		590,124
8.00%, 12/31/26(a)(b)			443		420,446
Empresa Nacional de Telecomunicaciones SA, 4.75%, 08/01/26(a)			6,698		7,438,966
Frontier Communications Corp.
10.50%, 09/15/22(g)(k)			1,300		888,875
5.88%, 10/15/27(a)			2,000		2,120,000
5.00%, 05/01/28(a)			867		882,935
6.75%, 05/01/29(a)			3,632		3,830,670
Globe Telecom, Inc.
2.50%, 07/23/30			221		208,776
3.00%, 07/23/35			910		834,925
Level 3 Financing, Inc.
5.25%, 03/15/26			2,579		2,656,370
4.63%, 09/15/27(a)			597		614,414
4.25%, 07/01/28(a)			8,811		8,910,652
3.63%, 01/15/29(a)			6,525		6,321,094
Liquid Telecommunications Financing PLC,
5.50%, 09/04/26(a)			2,632		2,770,180
Network i2i Ltd., 5.65%(l)			700		739,156
Oi SA, (10.00% Cash or 12.00% (8.00% Cash + 4.00% PIK), 10.00%, 07/27/25(i)			3,442		3,596,890
UPC Holding BV, 5.50%, 01/15/28(a)			1,479		1,528,473
VEON Holdings BV, 3.38%, 11/25/27(a)			3,501		3,434,306
Verizon Communications, Inc.
4.13%, 03/16/27(e)			14,716		16,672,195
4.33%, 09/21/28			4,435		5,077,492
3.88%, 02/08/29			9,803		10,905,316
4.02%, 12/03/29			7,081		7,920,465
3.15%, 03/22/30			13,692		14,441,310
1.50%, 09/18/30			15,867		14,567,682
1.68%, 10/30/30(a)			9,631		8,935,028
1.75%, 01/20/31			7,242		6,744,001
2.55%, 03/21/31			2,849		2,846,415
4.27%, 01/15/36			36,007		40,698,132
4.86%, 08/21/46			7,182		8,615,855
3.55%, 03/22/51			3,586		3,580,968
3.70%, 03/22/61			11,835		11,694,369
Ziggo BV
5.50%, 01/15/27(a)			4,652		4,843,895
4.88%, 01/15/30(a)			1,372		1,402,369
					380,005,424
Electric Utilities — 2.2%
Adani Electricity Mumbai Ltd., 3.95%, 02/12/30			1,919		1,931,593

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 47

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Electric Utilities (continued)
Adani Transmission Ltd. 4.00%, 08/03/26	USD		662	$	706,380
4.25%, 05/21/36			1,198		1,234,989
AEP Texas, Inc. 3.95%, 06/01/28			10,571		11,695,989
Series H, 3.45%, 01/15/50			1,440		1,404,852
AEP Transmission Co. LLC 4.25%, 09/15/48			2,195		2,524,426
3.80%, 06/15/49(e)			4,475		4,844,195
3.15%, 09/15/49			3,515		3,432,925
Series M, 3.65%, 04/01/50			5,215		5,531,646
Alabama Power Co. 6.00%, 03/01/39			215		292,534
3.75%, 03/01/45			6,806		7,261,957
3.45%, 10/01/49			1,012		1,031,872
Baltimore Gas & Electric Co. 3.50%, 08/15/46			4,197		4,285,526
3.75%, 08/15/47			2,530		2,706,169
3.20%, 09/15/49			3,823		3,712,188
2.90%, 06/15/50			4,364		4,035,204
Capex SA, 6.88%, 05/15/24(a)			1,158		1,017,954
CenterPoint Energy Houston Electric LLC 2.35%, 04/01/31			3,260		3,260,945
3.55%, 08/01/42			2,240		2,352,055
3.95%, 03/01/48			549		609,243
3.35%, 04/01/51			5,385		5,414,713
Commonwealth Edison Co. 4.70%, 01/15/44			3,000		3,570,590
3.13%, 03/15/51			3,050		2,959,146
DTE Electric Co. 3.95%, 03/01/49			3,229		3,609,211
Series A, 4.05%, 05/15/48			6,639		7,521,006
Duke Energy Carolinas LLC 3.95%, 11/15/28			1,701		1,914,066
2.45%, 02/01/30			9,938		10,003,068
3.75%, 06/01/45			1,177		1,258,782
3.88%, 03/15/46			3,172		3,423,549
3.70%, 12/01/47			5,364		5,698,014
Duke Energy Florida LLC 3.80%, 07/15/28			2,807		3,112,976
2.50%, 12/01/29			21,814		22,245,580
3.40%, 10/01/46			2,103		2,139,525
4.20%, 07/15/48			53		60,688
Duke Energy Ohio, Inc., 3.65%, 02/01/29			9,148		9,947,996
Duke Energy Progress LLC, 3.45%, 03/15/29			10,281		11,175,407
Edison International 2.40%, 09/15/22			139		141,748
3.13%, 11/15/22			10		10,335
3.55%, 11/15/24			3,527		3,789,724
4.95%, 04/15/25			4,907		5,477,265
Entergy Arkansas LLC, 4.20%, 04/01/49			1,197		1,340,896
Entergy Louisiana LLC, 4.20%, 09/01/48			7,609		8,568,593
Exelon Corp. 4.95%, 06/15/35			530		624,427
5.10%, 06/15/45			1,023		1,268,282
4.45%, 04/15/46			2,175		2,493,285
FEL Energy VI Sarl, 5.75%, 12/01/40			5,696		5,809,920
FirstEnergy Corp. 2.05%, 03/01/25			1,392		1,399,197
2.65%, 03/01/30			7,667		7,290,885
Series B, 4.40%, 07/15/27			9,423		10,129,725
Series B, 2.25%, 09/01/30			2,734		2,535,785

Security		Par (000)		Value
Electric Utilities (continued)
FirstEnergy Corp.
Series C, 3.40%, 03/01/50	USD		4,237	$	3,707,375
FirstEnergy Transmission LLC 4.35%, 01/15/25(a)			13,860		15,024,224
5.45%, 07/15/44(a)			1,121		1,295,159
4.55%, 04/01/49(a)			16,508		17,408,554
Florida Power & Light Co. 3.70%, 12/01/47			3,662		3,980,536
3.95%, 03/01/48			7,001		7,985,498
4.13%, 06/01/48			2,000		2,329,787
3.15%, 10/01/49			12,142		12,219,883
Generacion Mediterranea SA/Generacion Frias SA/Central Termica Roca SA, 9.63%, 07/27/23(a)			4,333		2,858,426
Huachen Energy Co. Ltd., 6.63%, 05/18/20(g)(k)			200		76,938
India Green Power Holdings, 4.00%, 02/22/27			630		629,803
ITC Holdings Corp., 2.70%, 11/15/22			3,406		3,515,391
LLPL Capital Pte Ltd., 6.88%, 02/04/39			593		690,983
MidAmerican Energy Co. 3.10%, 05/01/27			390		422,667
3.65%, 04/15/29			13,756		15,259,150
3.65%, 08/01/48			1,020		1,078,639
4.25%, 07/15/49			4,426		5,198,219
3.15%, 04/15/50			3,370		3,311,873
Mong Duong Finance Holdings BV, 5.13%, 05/07/29			796		797,741
Northern States Power Co. 2.25%, 04/01/31			4,010		4,005,043
3.40%, 08/15/42			3,707		3,840,737
4.00%, 08/15/45			1,610		1,808,579
2.90%, 03/01/50			2,475		2,364,220
2.60%, 06/01/51			2,448		2,192,125
3.20%, 04/01/52			2,500		2,506,311
NRG Energy, Inc., 2.45%, 12/02/27(a)			11,067		11,000,238
NSTAR Electric Co., 3.95%, 04/01/30			642		721,422
Ohio Power Co. 4.00%, 06/01/49			3,666		4,093,628
Series G, 6.60%, 02/15/33			3,415		4,576,959
Oncor Electric Delivery Co. LLC 3.70%, 11/15/28			5,350		5,933,434
5.30%, 06/01/42			597		769,965
3.80%, 09/30/47			2,314		2,491,094
4.10%, 11/15/48			606		686,848
3.80%, 06/01/49			3,582		3,894,388
3.10%, 09/15/49			3,583		3,478,431
PECO Energy Co., 3.05%, 03/15/51			6,773		6,617,983
Public Service Electric and Gas Co. 3.65%, 09/01/28			6,843		7,577,913
3.85%, 05/01/49			3,410		3,776,163
2.05%, 08/01/50			363		292,036
3.00%, 03/01/51			403		387,860
Southern California Edison Co. 1.85%, 02/01/22			1,203		1,204,345
2.25%, 06/01/30			12,939		12,526,239
4.00%, 04/01/47			2,328		2,398,104
Series A, 4.20%, 03/01/29			1,808		2,009,815
Series E, 3.70%, 08/01/25			10,666		11,648,827
Southwestern Public Service Co., 3.15%, 05/01/50			5,505		5,359,575
Star Energy Geothermal Darajat II/Star Energy Geothermal Salak 4.85%, 10/14/38(a)			3,000		3,266,250

48 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Electric Utilities (continued)
Star Energy Geothermal Darajat II/Star Energy Geothermal Salak 4.85%, 10/14/38	USD		2,225	$	2,422,469
Tampa Electric Co.
4.30%, 06/15/48			1,207		1,363,105
4.45%, 06/15/49			2,671		3,102,875
Trans-Allegheny Interstate Line Co., 3.85%, 06/01/25(a)			18,145		19,470,016
Vistra Operations Co. LLC
3.55%, 07/15/24(a)			2,129		2,227,856
5.50%, 09/01/26(a)			2,942		3,048,648
5.63%, 02/15/27(a)			3,811		3,961,077
5.00%, 07/31/27(a)			3,804		3,918,196
4.30%, 07/15/29(a)			13,729		14,509,227
					472,049,873
Electrical Equipment — 0.1%
Carrier Global Corp., 2.24%, 02/15/25			25,571		26,477,443
Suzlon Energy Ltd., (1.25% Cash and 2.75% PIK), Series SUEL, 4.00%, 08/17/32(i)(j)			160		240,000
					26,717,443
Electronic Equipment, Instruments & Components — 0.0%
Corning, Inc., 4.38%, 11/15/57			3,213		3,509,117
Energy Equipment & Services — 0.1%
Bristow Group, Inc., 6.88%, 03/01/28(a)			2,675		2,666,333
Hilong Holding Ltd., 8.25%, 09/26/22(g)(k)			250		189,922
Pioneer Energy Services Corp.
(11.00% Cash or 11.00% PIK), 11.00%, 05/15/25(a)(b)(i)			2,939		2,935,623
(5.00% Cash or 5.00% PIK), 5.00%, 11/15/25(a)(b)(i)(j)			2,081		2,080,894
Transocean Phoenix 2 Ltd., 7.75%, 10/15/24(a)			6,974		6,765,168
Transocean Proteus Ltd., 6.25%, 12/01/24(a)			700		665,190
					15,303,130
Equity Real Estate Investment Trusts (REITs) — 1.3%
American Tower Corp.
5.00%, 02/15/24			4,536		5,061,329
3.38%, 05/15/24			10		10,721
2.40%, 03/15/25			18,526		19,327,529
1.30%, 09/15/25			2,341		2,330,910
1.60%, 04/15/26			928		930,116
3.95%, 03/15/29			1,825		2,009,074
3.80%, 08/15/29			12,257		13,344,871
2.10%, 06/15/30			1,794		1,707,158
Boston Properties LP, 3.13%, 09/01/23			512		538,999
CC Holdings GS V LLC/Crown Castle GS III Corp., 3.85%, 04/15/23			2,211		2,354,131
Crown Castle International Corp.
1.35%, 07/15/25			2,608		2,602,541
4.45%, 02/15/26			2,370		2,669,051
3.70%, 06/15/26			1,551		1,696,690
1.05%, 07/15/26			10,560		10,224,476
4.30%, 02/15/29			1,324		1,484,088
3.10%, 11/15/29			16,276		16,800,067
3.30%, 07/01/30			6,417		6,716,968
2.25%, 01/15/31			3,936		3,783,076
2.10%, 04/01/31			2,991		2,824,028
4.00%, 11/15/49			3,044		3,162,238
Digital Dutch Finco BV
1.50%, 03/15/30	EUR		6,150		7,599,698
1.00%, 01/15/32			5,050		5,869,546
Duke Realty LP, 1.75%, 02/01/31	USD		12,762		11,854,242

Security		Par (000)		Value
Equity Real Estate Investment Trusts (REITs) (continued)
Equinix, Inc.
1.25%, 07/15/25	USD		2,633	$	2,610,948
1.00%, 09/15/25			11,613		11,403,261
GLP Capital LP/GLP Financing II, Inc.
5.75%, 06/01/28			3,074		3,546,074
4.00%, 01/15/30			6,163		6,411,061
4.00%, 01/15/31			11,274		11,651,397
Iron Mountain, Inc.
4.88%, 09/15/27(a)			1,000		1,023,125
5.00%, 07/15/28(a)			2,500		2,556,250
LMIRT Capital Pte Ltd., 7.25%, 06/19/24			200		204,188
MGM Growth Properties Operating Partnership LP/MGP Finance Co-Issuer, Inc.
5.63%, 05/01/24			6,235		6,692,451
4.63%, 06/15/25(a)			802		845,869
4.50%, 09/01/26			1,730		1,810,601
5.75%, 02/01/27			4,235		4,668,812
MPT Operating Partnership LP/MPT Finance Corp.
5.25%, 08/01/26			299		308,718
5.00%, 10/15/27			4,705		4,949,684
4.63%, 08/01/29			537		564,940
National Retail Properties, Inc.
2.50%, 04/15/30(e)			4,195		4,113,481
3.50%, 04/15/51			4,147		4,072,355
Park Intermediate Holdings LLC/PK Domestic Property LLC/PK Finance Co-Issuer, 5.88%, 10/01/28(a)			567		601,162
Prologis Euro Finance LLC, 1.50%, 09/10/49	EUR		7,300		8,310,138
Realty Income Corp.
3.00%, 01/15/27	USD		95		100,858
3.25%, 01/15/31			6,356		6,709,238
RHP Hotel Properties LP/RHP Finance Corp., 4.75%, 10/15/27			2,358		2,413,696
Service Properties Trust
5.00%, 08/15/22			4,481		4,547,901
4.50%, 06/15/23			7,725		7,847,518
4.35%, 10/01/24			1,505		1,496,176
7.50%, 09/15/25			1,479		1,680,768
5.50%, 12/15/27			790		835,609
VICI Properties LP/VICI Note Co., Inc.
3.50%, 02/15/25(a)			26,650		27,133,031
4.25%, 12/01/26(a)			13,700		14,016,264
3.75%, 02/15/27(a)			4,326		4,326,000
4.63%, 12/01/29(a)			597		619,304
4.13%, 08/15/30(a)			5,173		5,218,005
XHR LP, 6.38%, 08/15/25(a)			1,392		1,470,300
					279,660,730
Food & Staples Retailing — 0.5%
Albertsons Cos., Inc./Safeway, Inc./New Albertsons LP/Albertsons LLC
3.50%, 02/15/23(a)			3,289		3,354,780
5.75%, 03/15/25			1,227		1,267,123
7.50%, 03/15/26(a)			3,937		4,348,869
4.63%, 01/15/27(a)			806		835,375
5.88%, 02/15/28(a)			3,317		3,536,751
4.88%, 02/15/30(a)			597		613,716
Alimentation Couche-Tard, Inc., 3.55%, 07/26/27(a)			12,317		13,368,668
CVS Health Corp.
3.25%, 08/15/29			27,811		29,396,064
3.75%, 04/01/30			26,721		29,148,989

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 49

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Food & Staples Retailing (continued)
CVS Health Corp. 5.13%, 07/20/45	USD		12,144	$	14,867,305
Performance Food Group, Inc., 5.50%, 10/15/27(a)			3,012		3,149,829
					103,887,469
Food Products — 0.3%
BRF GmbH, 4.35%, 09/29/26(a)			2,245		2,296,214
BRF SA 4.88%, 01/24/30(a)			594		605,301
5.75%, 09/21/50(a)			3,269		3,207,379
Campbell Soup Co., 8.88%, 05/01/21			2,350		2,364,436
CP Foods Capital Ltd., 0.50%, 06/18/25(j)			400		421,924
Darling Ingredients, Inc., 5.25%, 04/15/27(a)			1,690		1,776,612
JBS Investments II GmbH 7.00%, 01/15/26(a)			3,405		3,624,350
5.75%, 01/15/28(a)			2,508		2,645,940
JBS USA LUX SA/JBS USA Finance, Inc., 6.75%, 02/15/28(a)			4,011		4,382,017
JBS USA LUX SA/JBS USA Food Co./JBS USA Finance, Inc.
6.50%, 04/15/29(a)			4,974		5,618,133
5.50%, 01/15/30(a)			746		825,632
Knight Castle Investments Ltd., 7.99%(g)(k)			700		488,906
Lamb Weston Holdings, Inc. 4.63%, 11/01/24(a)			2,776		2,880,711
4.88%, 11/01/26(a)			2,790		2,885,557
MHP Lux SA, 6.25%, 09/19/29(a)			594		588,803
Mondelez International, Inc., 2.75%, 04/13/30			7,714		7,875,507
Pilgrim’s Pride Corp., 5.88%, 09/30/27(a)			5,344		5,727,165
Post Holdings, Inc. 5.75%, 03/01/27(a)			3,722		3,914,651
5.63%, 01/15/28(a)			2,728		2,870,483
5.50%, 12/15/29(a)			2,156		2,308,645
Zhou Hei Ya International Holdings Co. Ltd., 1.00%, 11/05/25(j)	HKD		3,000		398,049
					57,706,415
Gas Utilities — 0.1%
Atmos Energy Corp. 4.13%, 03/15/49	USD		206		228,665
3.38%, 09/15/49			2,876		2,858,696
ONE Gas, Inc., 2.00%, 05/15/30			2,235		2,113,755
Piedmont Natural Gas Co., Inc. 2.50%, 03/15/31			4,895		4,844,680
3.64%, 11/01/46			427		432,828
Promigas SA ESP/Gases del Pacifico SAC 3.75%, 10/16/29(a)			790		798,888
3.75%, 10/16/29			1,460		1,476,425
					12,753,937
Health Care Equipment & Supplies — 0.1%
Boston Scientific Corp., 2.65%, 06/01/30			7,654		7,724,998
Medtronic Global Holdings SCA 1.50%, 07/02/39	EUR		3,660		4,466,135
1.38%, 10/15/40			570		678,995
1.75%, 07/02/49			3,500		4,332,025
Teleflex, Inc., 4.63%, 11/15/27	USD		1,667		1,764,936
					18,967,089
Health Care Providers & Services — 1.3%
Aetna, Inc. 4.50%, 05/15/42			2,558		2,914,337
4.75%, 03/15/44			1,023		1,197,422
AMN Healthcare, Inc., 4.63%, 10/01/27(a)			2,029		2,074,652

Security		Par (000)		Value
Health Care Providers & Services (continued)
Anthem, Inc. 3.65%, 12/01/27	USD		7,853	$	8,666,024
3.60%, 03/15/51			4,953		5,126,880
Centene Corp. 5.38%, 06/01/26(a)			12,003		12,551,537
5.38%, 08/15/26(a)			2,500		2,637,250
4.25%, 12/15/27			8,294		8,724,262
4.63%, 12/15/29			2,090		2,262,017
Cigna Corp. 3.25%, 04/15/25			4,621		4,970,472
3.40%, 03/01/27			6,443		6,995,428
4.38%, 10/15/28			18,515		21,182,413
DaVita, Inc., 4.63%, 06/01/30(a)			6,689		6,815,154
DH Europe Finance II S.a.r.l, 1.80%, 09/18/49	EUR		3,600		4,466,664
Encompass Health Corp. 4.50%, 02/01/28	USD		1,372		1,405,093
4.75%, 02/01/30			1,382		1,421,665
HCA, Inc. 4.75%, 05/01/23			17,963		19,361,282
5.00%, 03/15/24			15,322		17,048,079
5.38%, 02/01/25			1,552		1,731,279
5.25%, 04/15/25			25,546		29,171,168
5.88%, 02/15/26			896		1,027,040
5.25%, 06/15/26			7,614		8,751,213
5.38%, 09/01/26			597		673,117
5.63%, 09/01/28			896		1,030,400
5.88%, 02/01/29			597		695,505
Humana, Inc. 4.50%, 04/01/25			4,430		4,976,765
3.13%, 08/15/29			2,294		2,392,807
4.88%, 04/01/30			2,923		3,435,053
Molina Healthcare, Inc., 5.38%, 11/15/22			2,368		2,482,943
Select Medical Corp., 6.25%, 08/15/26(a)			16,871		17,929,824
Tenet Healthcare Corp. 4.63%, 07/15/24			4,979		5,082,015
4.63%, 09/01/24(a)			9,353		9,621,899
5.13%, 05/01/25			8,459		8,577,849
4.88%, 01/01/26(a)			15,230		15,835,545
6.25%, 02/01/27(a)			9,396		9,920,907
5.13%, 11/01/27(a)			896		936,947
4.63%, 06/15/28(a)			511		523,765
UnitedHealth Group, Inc. 2.95%, 10/15/27			5,785		6,209,678
3.85%, 06/15/28			863		968,816
2.75%, 05/15/40			6,062		5,960,373
4.63%, 11/15/41			3,918		4,844,146
4.75%, 07/15/45			4,326		5,451,380
3.75%, 10/15/47			1,148		1,254,703
					279,305,768
Hotels, Restaurants & Leisure — 0.9%
1011778 BC ULC/New Red Finance, Inc., 3.88%, 01/15/28(a)			448		452,812
Affinity Gaming, 6.88%, 12/15/27(a)			2,092		2,204,445
Aramark Services, Inc. 4.75%, 06/01/26			1,657		1,703,396
5.00%, 02/01/28(a)			3,857		4,002,602
Boyd Gaming Corp. 8.63%, 06/01/25(a)			1,656		1,841,472
6.38%, 04/01/26			1,848		1,908,060
6.00%, 08/15/26			1,726		1,797,069
Caesars Entertainment, Inc. 6.25%, 07/01/25(a)			13,890		14,806,948

50 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Hotels, Restaurants & Leisure (continued)
Caesars Entertainment, Inc. 8.13%, 07/01/27(a)	USD		4,331	$	4,775,989
Caesars Resort Collection LLC/CRC Finco, Inc., 5.25%, 10/15/25(a)			4,652		4,669,143
Carnival Corp., 11.50%, 04/01/23(a)			2,510		2,877,087
Cedar Fair LP, 5.25%, 07/15/29			3,581		3,680,874
Cedar Fair LP/Canada’s Wonderland Co./Magnum Management Corp./Millennium Op
5.50%, 05/01/25(a)			6,059		6,377,340
5.38%, 04/15/27			3,117		3,194,925
Champion Path Holdings Ltd. 4.50%, 01/27/26			320		332,700
4.85%, 01/27/28			200		208,910
Churchill Downs, Inc. 5.50%, 04/01/27(a)			3,722		3,890,234
4.75%, 01/15/28(a)			1,701		1,759,234
Colt Merger Sub, Inc., 5.75%, 07/01/25(a)			2,601		2,744,835
Full House Resorts, Inc., 8.25%, 02/15/28(a)			505		537,977
Golden Nugget, Inc., 6.75%, 10/15/24(a)			3,550		3,589,653
Haidilao International Holding Ltd., 2.15%, 01/14/26			970		958,691
Hilton Domestic Operating Co., Inc., 4.88%, 01/15/30			597		633,298
Hilton Worldwide Finance LLC/Hilton Worldwide Finance Corp., 4.88%, 04/01/27			2,561		2,673,044
HIS Co. Ltd., 0.00%, 11/15/24(j)(m)	JPY		40,000		314,122
Hyatt Hotels Corp., 5.38%, 04/23/25	USD		4,131		4,634,835
International Game Technology PLC 6.50%, 02/15/25(a)			3,422		3,755,645
6.25%, 01/15/27(a)			448		496,359
IRB Holding Corp., 7.00%, 06/15/25(a)			1,742		1,875,176
Marriott International, Inc. 4.63%, 06/15/30			2,084		2,331,362
2.85%, 04/15/31			4,417		4,335,051
Marriott Ownership Resorts, Inc., 6.13%, 09/15/25(a)			3,879		4,119,995
Marriott Ownership Resorts, Inc./ILG LLC, 6.50%, 09/15/26			3,289		3,434,949
McDonald’s Corp. 2.13%, 03/01/30			3,710		3,622,308
3.60%, 07/01/30			8,935		9,745,923
4.60%, 05/26/45			2,222		2,597,913
4.88%, 12/09/45			5,602		6,781,446
4.45%, 09/01/48			2,753		3,210,398
Melco Resorts Finance Ltd. 5.63%, 07/17/27			200		209,000
5.38%, 12/04/29(a)			537		565,864
MGM China Holdings Ltd. 5.38%, 05/15/24(a)			2,481		2,556,981
5.88%, 05/15/26(a)			2,506		2,623,469
5.88%, 05/15/26			200		209,375
MGM Resorts International 5.75%, 06/15/25			392		427,280
4.63%, 09/01/26			229		240,142
5.50%, 04/15/27			390		419,250
Peninsula Pacific Entertainment LLC/Peninsula Pacific Entertainment Finance In, 8.50%, 11/15/27(a)			8,106		8,713,950
REXLot Holdings Ltd., 4.50%, 04/17/19(g)(j)(k)	HKD		1,161		1,493
Sands China Ltd., 4.38%, 06/18/30	USD		1,962		2,077,836

Security		Par (000)		Value
Hotels, Restaurants & Leisure (continued)
Scientific Games International, Inc., 5.00%, 10/15/25(a)	USD		3,693	$	3,824,840
SeaWorld Parks & Entertainment, Inc. 8.75%, 05/01/25(a)			4,134		4,475,055
9.50%, 08/01/25(a)			1,587		1,724,791
Starbucks Corp. 2.25%, 03/12/30			6,381		6,276,371
2.55%, 11/15/30			8,838		8,855,526
Station Casinos LLC, 5.00%, 10/01/25(a)			791		800,888
Wyndham Destinations, Inc., 6.63%, 07/31/26(a)			1,141		1,295,434
Wyndham Hotels & Resorts, Inc., 5.38%, 04/15/26(a)			1,681		1,718,822
Wynn Las Vegas LLC/Wynn Las Vegas Capital Corp.
5.50%, 03/01/25(a)			6,222		6,573,543
5.25%, 05/15/27(a)			3,101		3,247,150
Wynn Macau Ltd. 4.88%, 10/01/24(a)			3,585		3,630,933
5.50%, 01/15/26			200		208,000
5.50%, 10/01/27(a)			2,511		2,608,301
5.50%, 10/01/27			400		415,500
5.13%, 12/15/29(a)			597		608,940
Wynn Resorts Finance LLC/Wynn Resorts Capital Corp.
7.75%, 04/15/25(a)			5,371		5,822,621
5.13%, 10/01/29(a)			5,182		5,303,777
					198,311,352
Household Durables — 0.4%
Ashton Woods USA LLC/Ashton Woods Finance Co.
6.75%, 08/01/25(a)			1,069		1,103,743
9.88%, 04/01/27(a)			3,448		3,870,380
6.63%, 01/15/28(a)			6,260		6,666,900
Beazer Homes U.S.A., Inc., 7.25%, 10/15/29			4,961		5,407,490
Brookfield Residential Properties, Inc./Brookfield Residential U.S. Corp., 6.25%, 09/15/27(a)			6,893		7,194,569
Century Communities, Inc., 6.75%, 06/01/27			7,145		7,594,706
KB Home, 7.63%, 05/15/23			1,769		1,917,154
Lennar Corp. 4.13%, 01/15/22			1,350		1,370,925
4.50%, 04/30/24			1,533		1,667,551
5.88%, 11/15/24			4,092		4,644,420
4.75%, 05/30/25			299		333,011
5.25%, 06/01/26			60		68,822
4.75%, 11/29/27			537		616,540
LGI Homes, Inc., 6.88%, 07/15/26(a)			1,069		1,115,769
M/I Homes, Inc., 4.95%, 02/01/28			5,263		5,450,494
Mattamy Group Corp. 5.25%, 12/15/27(a)			3,110		3,253,837
4.63%, 03/01/30(a)			3,535		3,511,245
New Home Co., Inc., 7.25%, 10/15/25(a)			1,272		1,316,787
PulteGroup, Inc. 5.50%, 03/01/26			193		225,188
5.00%, 01/15/27			288		331,200
6.00%, 02/15/35			53		66,250
Taylor Morrison Communities, Inc., 5.88%, 06/15/27(a)			299		330,395
Tempur Sealy International, Inc., 5.50%, 06/15/26			3,695		3,828,944
Toll Brothers Finance Corp. 4.38%, 04/15/23			5,264		5,500,880

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 51

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Household Durables (continued)
Toll Brothers Finance Corp. 3.80%, 11/01/29	USD		5,508	$	5,817,825
TRI Pointe Group, Inc. 5.25%, 06/01/27			2,378		2,544,460
5.70%, 06/15/28			333		368,035
Weekley Homes LLC/Weekley Finance Corp., 4.88%, 09/15/28(a)			1,891		1,938,275
					78,055,795
Household Products — 0.0%
Spectrum Brands, Inc., 5.75%, 07/15/25			2,442		2,518,313
Independent Power and Renewable Electricity Producers — 0.3%
Calpine Corp. 5.25%, 06/01/26(a)			5,537		5,693,420
4.50%, 02/15/28(a)			15,793		15,925,661
Colbun SA, 3.15%, 03/06/30(a)			675		690,609
Continuum Energy Levanter Pte Ltd., 4.50%, 02/09/27(a)			2,175		2,207,625
Genneia SA, 8.75%, 01/20/22			2,840		2,525,825
India Green Energy Holdings, 5.38%, 04/29/24(a)			2,200		2,285,250
NRG Energy, Inc. 2.00%, 12/02/25(a)			3,282		3,281,451
7.25%, 05/15/26			2,988		3,107,520
6.63%, 01/15/27			3,611		3,755,440
5.75%, 01/15/28			2,423		2,574,438
5.25%, 06/15/29(a)			2,170		2,321,900
2.75%, 06/01/48(j)			200		232,967
Orazul Energy Egenor S en C por A, 5.63%, 04/28/27(a)			607		632,229
ReNew Power Pvt Ltd., 5.88%, 03/05/27			200		212,188
ReNew Power Synthetic, 6.67%, 03/12/24			1,000		1,050,625
Star Energy Geothermal Wayang Windu Ltd., 6.75%, 04/24/33(a)			181		202,544
Stoneway Capital Corp. 10.00%, 03/01/27(g)(k)			4,059		1,598,084
10.00%, 03/01/27(a)(g)(k)			4,327		1,703,740
Talen Energy Supply LLC 6.50%, 06/01/25			1,999		1,605,447
7.25%, 05/15/27(a)			3,184		3,255,194
					54,862,157
Industrial Conglomerates — 0.2%
General Electric Co., 5.88%, 01/14/38			19,050		24,651,970
Grupo KUO SAB De CV, 5.75%, 07/07/27(a)			2,142		2,247,092
Roper Technologies, Inc., 2.95%, 09/15/29			4,177		4,349,886
Tyco Electronics Group SA, 3.45%, 08/01/24			865		931,951
					32,180,899
Insurance — 0.4%
Ambac Assurance Corp., 5.10%(a)(l)			462		633,218
Ambac LSNI LLC, (3 mo. LIBOR US + 5.00%), 6.00%, 02/12/23(a)(d)			2,476		2,482,547
American International Group, Inc. 3.40%, 06/30/30			11,346		12,060,330
4.50%, 07/16/44			5,835		6,606,480
4.38%, 01/15/55			3,445		3,844,388
Aon Corp. 4.50%, 12/15/28			5,621		6,436,362
3.75%, 05/02/29			13,865		15,255,699
2.80%, 05/15/30			7,275		7,434,250
Aon PLC, 4.75%, 05/15/45			95		115,289
Marsh & McLennan Cos., Inc. 1.35%, 09/21/26	EUR		4,390		5,453,247

Security		Par (000)		Value
Insurance (continued)
Marsh & McLennan Cos., Inc. 4.38%, 03/15/29	USD		1,454	$	1,667,049
1.98%, 03/21/30	EUR		3,035		3,984,000
2.25%, 11/15/30	USD		15,034		14,761,425
Nippon Life Insurance Co., 2.75%, 01/21/51			937		888,979
QBE Insurance Group Ltd., 5.88%, 06/17/46			450		489,980
Union Life Insurance Co. Ltd., 3.00%, 09/19/21			229		217,121
Willis North America, Inc., 3.60%, 05/15/24			2,050		2,209,203
ZhongAn Online P&C Insurance Co. Ltd. 3.13%, 07/16/25			700		705,687
3.50%, 03/08/26			1,200		1,220,625
					86,465,879
Interactive Media & Services — 0.0%
Baidu, Inc., 4.38%, 05/14/24			3,320		3,643,011
Tencent Holdings Ltd., 3.24%, 06/03/50			2,350		2,155,726
					5,798,737
Internet & Direct Marketing Retail — 0.2%
Alibaba Group Holding Ltd., 3.60%, 11/28/24			5,095		5,515,796
Amazon.com, Inc., 3.88%, 08/22/37			8,229		9,428,636
Baozun, Inc., 1.63%, 05/01/24(j)			258		265,901
Booking Holdings, Inc., 4.10%, 04/13/25			11,596		12,921,144
Expedia Group, Inc. 6.25%, 05/01/25(a)			2,306		2,667,378
3.25%, 02/15/30			3,840		3,864,752
Netflix, Inc. 4.88%, 04/15/28			955		1,080,344
6.38%, 05/15/29			478		592,720
5.38%, 11/15/29(a)			537		635,029
4.88%, 06/15/30(a)			597		687,469
					37,659,169
IT Services — 0.9%
21Vianet Group, Inc., 7.88%, 10/15/21			685		696,987
Atento Luxco 1 SA, 8.00%, 02/10/26(a)			1,010		1,059,869
Fidelity National Information Services, Inc. 1.00%, 12/03/28	EUR		10,500		12,653,297
2.95%, 05/21/39			4,400		6,231,071
Fiserv, Inc. 3.20%, 07/01/26	USD		3,974		4,289,290
3.50%, 07/01/29			28,912		31,184,462
2.65%, 06/01/30			6,790		6,838,370
Global Payments, Inc. 4.80%, 04/01/26			13,857		15,845,755
4.45%, 06/01/28			2,703		3,099,502
3.20%, 08/15/29			7,871		8,289,827
International Business Machines Corp. 3.30%, 05/15/26			18,911		20,597,824
1.95%, 05/15/30			25,671		24,849,563
2.85%, 05/15/40			3,712		3,578,366
Leidos, Inc., 4.38%, 05/15/30(a)			13,524		15,033,819
Mastercard, Inc., 2.95%, 06/01/29			14,690		15,751,730
Meituan, 3.05%, 10/28/30			805		782,862
PayPal Holdings, Inc. 1.65%, 06/01/25			4,546		4,629,662
2.65%, 10/01/26			28		29,628
Visa, Inc. 4.15%, 12/14/35			7,727		9,136,052
2.70%, 04/15/40			5,741		5,622,343
					190,200,279
Leisure Products — 0.1%
Hasbro, Inc., 2.60%, 11/19/22			12,338		12,726,185

52 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Life Sciences Tools & Services — 0.2%
Agilent Technologies, Inc. 3.05%, 09/22/26	USD		9,644	$	10,309,466
2.75%, 09/15/29			5,154		5,276,984
2.10%, 06/04/30			3,339		3,266,401
Charles River Laboratories International, Inc., 4.25%, 05/01/28(a)			758		780,740
IQVIA, Inc. 5.00%, 10/15/26(a)			3,518		3,654,323
5.00%, 05/15/27(a)			3,707		3,913,832
Jaguar Holding Co. II/PPD Development LP, 5.00%, 06/15/28(a)			904		941,516
Thermo Fisher Scientific, Inc. 4.50%, 03/25/30			3,496		4,070,158
1.88%, 10/01/49	EUR		7,400		9,169,883
					41,383,303
Machinery — 0.2%
China Conch Venture Holdings International Ltd., 0.00%, 09/05/23(j)(m)	HKD		6,000		885,088
Colfax Corp., 6.00%, 02/15/24(a)	USD		2,044		2,107,364
HTA Group Ltd., 7.00%, 12/18/25(a)			2,290		2,424,537
Otis Worldwide Corp., 2.57%, 02/15/30			7,771		7,826,916
Parker-Hannifin Corp., 2.70%, 06/14/24			9,940		10,539,636
Terex Corp., 5.63%, 02/01/25(a)			4,180		4,297,583
Vertical U.S. Newco, Inc., 5.25%, 07/15/27(a)			5,290		5,537,969
					33,619,093
Media — 1.9%
Altice France SA 7.38%, 05/01/26(a)			15,115		15,721,111
8.13%, 02/01/27(a)			5,275		5,781,927
5.50%, 01/15/28(a)			3,005		3,079,344
AMC Networks, Inc. 5.00%, 04/01/24			1,315		1,331,438
4.75%, 08/01/25			3,348		3,434,462
CCO Holdings LLC/CCO Holdings Capital Corp. 5.75%, 02/15/26(a)			3,990		4,116,682
5.50%, 05/01/26(a)			3,389		3,495,076
5.13%, 05/01/27(a)			8,329		8,806,377
5.88%, 05/01/27(a)			1,819		1,877,208
5.00%, 02/01/28(a)			10,487		11,091,576
5.38%, 06/01/29(a)			3,505		3,759,113
4.75%, 03/01/30(a)			4,054		4,200,957
Charter Communications Operating LLC/Charter Communications Operating Capital (3 mo. LIBOR US + 1.65%), 1.86%, 02/01/24(d)			208		213,678
6.38%, 10/23/35			4,051		5,246,014
6.48%, 10/23/45			18,393		23,947,894
5.38%, 05/01/47			11,668		13,544,237
5.75%, 04/01/48			42		51,061
5.13%, 07/01/49			11,527		12,968,693
4.80%, 03/01/50			2,630		2,821,241
Clear Channel Worldwide Holdings, Inc., 5.13%, 08/15/27(a)			3,843		3,865,097
Comcast Corp. 2.35%, 01/15/27			2,186		2,281,843
3.30%, 02/01/27			12,021		13,116,698
3.30%, 04/01/27			290		316,160
2.65%, 02/01/30			12,141		12,428,496
3.40%, 04/01/30			28,604		30,970,268
4.25%, 10/15/30			2,142		2,461,222
1.95%, 01/15/31			32,836		31,624,452
4.25%, 01/15/33			238		274,799

Security		Par (000)		Value
Media (continued)
Comcast Corp. 3.90%, 03/01/38	USD		11,314	$	12,707,978
4.60%, 10/15/38			41		49,491
3.75%, 04/01/40			2,938		3,223,586
4.60%, 08/15/45			549		663,729
3.40%, 07/15/46			6,070		6,276,682
4.00%, 08/15/47			445		497,565
3.97%, 11/01/47			8,345		9,318,664
2.45%, 08/15/52			2,750		2,351,387
2.65%, 08/15/62			1,525		1,293,890
Cox Communications, Inc. 3.25%, 12/15/22(a)			2,960		3,094,266
3.15%, 08/15/24(a)			19,141		20,437,629
CSC Holdings LLC 7.50%, 04/01/28(a)			3,177		3,503,596
5.75%, 01/15/30(a)			6,441		6,783,951
Diamond Sports Group LLC/Diamond Sports Finance Co., 5.38%, 08/15/26(a)			1,821		1,311,120
Discovery Communications LLC 1.90%, 03/19/27	EUR		10,803		13,598,660
4.13%, 05/15/29	USD		292		322,513
Gray Television, Inc. 5.88%, 07/15/26(a)			1,994		2,066,283
7.00%, 05/15/27(a)			2,255		2,452,313
iHeartCommunications, Inc. 6.38%, 05/01/26			3,559		3,776,740
5.25%, 08/15/27(a)			3,210		3,301,838
4.75%, 01/15/28(a)			299		301,243
Kakao Corp., 0.00%, 04/28/23(j)(m)			200		239,000
Lamar Media Corp., 3.75%, 02/15/28			358		357,553
Lions Gate Capital Holdings LLC, 5.50%, 04/15/29(a)			1,984		1,984,218
Meredith Corp., 6.88%, 02/01/26			2,871		2,952,608
Nexstar Broadcasting, Inc. 5.63%, 07/15/27(a)			3,217		3,371,802
4.75%, 11/01/28(a)			2,573		2,600,107
Nielsen Co. Luxembourg S.a.r.l, 5.00%, 02/01/25(a)			1,349		1,379,353
Omnicom Group, Inc., 2.45%, 04/30/30			2,639		2,610,545
Outfront Media Capital LLC/Outfront Media Capital Corp.
5.00%, 08/15/27(a)			4,648		4,694,480
4.63%, 03/15/30(a)			299		287,788
Sirius XM Radio, Inc. 4.63%, 07/15/24(a)			8,075		8,318,057
5.38%, 07/15/26(a)			2,752		2,841,440
5.00%, 08/01/27(a)			6,435		6,750,637
5.50%, 07/01/29(a)			4,240		4,584,500
TEGNA, Inc. 4.63%, 03/15/28			4,459		4,537,032
5.00%, 09/15/29			657		681,808
TWDC Enterprises 18 Corp. 3.70%, 12/01/42			2,383		2,580,630
3.00%, 07/30/46			2,724		2,622,612
ViacomCBS, Inc. 4.38%, 03/15/43			3,745		4,041,098
5.85%, 09/01/43			5,643		7,207,286
VTR Comunicaciones SpA, 4.38%, 04/15/29(a)			2,585		2,591,463
Walt Disney Co. 3.70%, 10/15/25			1,846		2,035,360
2.75%, 09/01/49			7,330		6,710,947

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 53

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Media (continued)
Walt Disney Co.
4.70%, 03/23/50	USD		4,729	$	5,926,286
Ziggo Bond Co. BV, 6.00%, 01/15/27(a)			1,779		1,854,608
					403,921,466
Metals & Mining — 0.2%
ABJA Investment Co. Pte Ltd., 5.95%, 07/31/24			200		215,688
Anglo American Capital PLC, 5.63%, 04/01/30(a)			6,417		7,667,962
AngloGold Ashanti Holdings PLC, 3.75%, 10/01/30			1,102		1,104,411
FMG Resources August 2006 Pty Ltd.
5.13%, 05/15/24(a)			327		354,424
4.50%, 09/15/27(a)			358		382,502
Freeport-McMoRan, Inc.
5.00%, 09/01/27			358		380,411
5.25%, 09/01/29			358		391,480
Fresnillo PLC, 4.25%, 10/02/50(a)			2,603		2,557,447
Metinvest BV, 8.50%, 04/23/26(a)			594		662,458
Newmont Corp.
2.80%, 10/01/29			4,682		4,811,813
2.25%, 10/01/30			4,592		4,473,237
Nucor Corp., 3.95%, 05/01/28			2,488		2,771,627
Periama Holdings LLC, 5.95%, 04/19/26			595		627,725
Steel Dynamics, Inc., 2.80%, 12/15/24			3,750		3,965,592
Vale Overseas Ltd., 3.75%, 07/08/30			2,475		2,573,752
Vedanta Resources Finance II PLC
8.00%, 04/23/23			900		821,574
13.88%, 01/21/24			200		215,812
8.95%, 03/11/25(a)			5,450		5,207,475
					39,185,390
Multiline Retail — 0.0%
Dollar General Corp., 4.13%, 04/03/50			296		327,880
Macy’s, Inc., 8.38%, 06/15/25(a)			1,000		1,105,770
					1,433,650
Multi-Utilities — 0.3%
Ameren Illinois Co.
3.80%, 05/15/28			3,671		4,051,768
3.25%, 03/15/50			3,650		3,665,827
CenterPoint Energy Resources Corp., 1.75%, 10/01/30			15,457		14,191,094
Consumers Energy Co.
3.25%, 08/15/46			628		626,228
3.75%, 02/15/50			5,099		5,624,648
3.10%, 08/15/50			6,026		5,928,339
3.50%, 08/01/51			3,600		3,789,173
Dominion Energy Gas Holdings LLC, 4.80%, 11/01/43			1,110		1,267,733
Eastern Energy Gas Holdings LLC, 4.60%, 12/15/44			1,268		1,416,307
Virginia Electric & Power Co.
4.00%, 01/15/43			8,631		9,582,106
Series A, 3.50%, 03/15/27			3,975		4,357,620
					54,500,843
Oil, Gas & Consumable Fuels — 2.8%
Blue Racer Midstream LLC/Blue Racer Finance Corp., 7.63%, 12/15/25(a)			945		1,018,445
Boardwalk Pipelines LP
4.80%, 05/03/29			640		707,484
3.40%, 02/15/31			3,031		3,028,590
BP Capital Markets America, Inc.
3.79%, 02/06/24			7,003		7,596,872

Security		Par (000)		Value
Oil, Gas & Consumable Fuels (continued)
BP Capital Markets America, Inc.
3.80%, 09/21/25	USD		4,087	$	4,503,103
3.41%, 02/11/26			1,150		1,250,316
BP Capital Markets PLC, 3.81%, 02/10/24			2,475		2,697,733
Bruin E&P Partners LLC, 8.88%, 08/01/23(b)(g)(k)			2,601		16,516
Buckeye Partners LP
4.15%, 07/01/23			1,988		2,040,185
4.35%, 10/15/24			2,500		2,568,750
4.13%, 03/01/25(a)			1,160		1,183,538
3.95%, 12/01/26			358		353,869
California Resources Corp., 7.13%, 02/01/26(a)			1,674		1,703,647
Cameron LNG LLC
3.30%, 01/15/35(a)			7,430		7,635,471
3.40%, 01/15/38(a)			11,339		11,434,483
Centennial Resource Production LLC, 5.38%, 01/15/26(a)			375		330,000
Cheniere Corpus Christi Holdings LLC
5.88%, 03/31/25			10,816		12,325,481
5.13%, 06/30/27			16,852		19,272,265
Cheniere Energy Partners LP
5.63%, 10/01/26			2,955		3,090,044
4.50%, 10/01/29			896		929,170
Cheniere Energy, Inc.
(4.88% Cash or 4.88% PIK) , 4.88%, 05/28/21(a)(i)(j)			16,446		16,485,103
4.63%, 10/15/28(a)			2,529		2,626,468
Chesapeake Energy Corp.
5.50%, 02/01/26(a)			1,644		1,711,231
0.00%, 02/15/26(b)(g)(k)			9,090		1
0.00%, 06/15/26(b)(g)(k)			425		—
0.00%, 08/15/26(b)(g)(k)			623		—
Chevron U.S.A., Inc.
4.95%, 08/15/47			4,422		5,559,667
2.34%, 08/12/50			3,650		3,033,507
CrownRock LP/CrownRock Finance, Inc., 5.63%, 10/15/25(a)			3,125		3,188,188
DCP Midstream Operating LP
5.38%, 07/15/25			493		534,227
5.13%, 05/15/29			358		380,715
Diamondback Energy, Inc., 3.50%, 12/01/29			16,942		17,583,231
Enbridge Energy Partners LP, 7.38%, 10/15/45			658		930,928
Enbridge, Inc., 2.90%, 07/15/22			2,018		2,075,187
Endeavor Energy Resources LP/EER Finance, Inc.
5.50%, 01/30/26(a)			1,718		1,782,940
5.75%, 01/30/28(a)			1,351		1,427,088
Energean Israel Finance Ltd., 5.88%, 03/30/31(a)			3,755		3,753,123
Energy Transfer Operating LP
3.60%, 02/01/23			4,230		4,405,155
4.25%, 03/15/23			7,941		8,380,568
7.60%, 02/01/24			2,846		3,268,348
4.05%, 03/15/25			2,850		3,079,406
2.90%, 05/15/25			18,413		19,160,901
6.50%, 02/01/42			6,240		7,441,422
Series 5Y, 4.20%, 09/15/23			3,200		3,426,808
Energy Transfer Partners LP/Regency Energy Finance Corp., 4.50%, 11/01/23			5,290		5,694,235
Enterprise Products Operating LLC
3.13%, 07/31/29			7,917		8,348,964
2.80%, 01/31/30			2,069		2,136,180

54 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Oil, Gas & Consumable Fuels (continued)
EOG Resources, Inc., 4.15%, 01/15/26	USD		9,444	$	10,606,706
Exxon Mobil Corp., 1.41%, 06/26/39	EUR		9,940		11,527,249
Galaxy Pipeline Assets BidCo. Ltd.
2.16%, 03/31/34(a)	USD		2,800		2,716,140
2.63%, 03/31/36			1,875		1,790,625
2.94%, 09/30/40(a)			3,170		3,063,805
Gray Oak Pipeline LLC
2.00%, 09/15/23(a)			4,753		4,838,015
2.60%, 10/15/25(a)			6,056		6,145,491
Great Western Petroleum LLC/Great Western Finance Corp., 12.00%, 09/01/25(a)			2,672		2,378,080
Hammerhead Resources, Inc., Series AI, 9.00%, 07/10/22(b)			2,844		2,843,787
HPCL-Mittal Energy Ltd., 5.45%, 10/22/26			200		209,250
Kinder Morgan Energy Partners LP
6.50%, 02/01/37			2,734		3,461,212
6.95%, 01/15/38			1,402		1,880,974
6.55%, 09/15/40			1,664		2,162,392
Leviathan Bond Ltd., 5.75%, 06/30/23(a)			2,336		2,445,940
Marathon Petroleum Corp.
4.75%, 09/15/44			1,372		1,521,745
5.85%, 12/15/45			1,915		2,270,001
Matador Resources Co., 5.88%, 09/15/26			627		610,541
Medco Platinum Road Pte Ltd., 6.75%, 01/30/25			200		208,750
MPLX LP
4.88%, 12/01/24			8,663		9,723,412
1.75%, 03/01/26			10,530		10,546,082
2.65%, 08/15/30			9,847		9,649,625
NGPL PipeCo LLC
4.38%, 08/15/22(a)			5,395		5,600,024
4.88%, 08/15/27(a)			7,707		8,615,310
7.77%, 12/15/37(a)			1,336		1,772,046
Northwest Pipeline LLC, 4.00%, 04/01/27			19,394		21,727,002
Odebrecht Offshore Drilling Finance Ltd., (7.72% Cash or 7.72% PIK), 7.72%, 12/01/26(a)(i)			1		132
Parsley Energy LLC/Parsley Finance Corp. 5.63%, 10/15/27(a)			643		696,851
4.13%, 02/15/28(a)			975		1,032,281
PBF Holding Co. LLC/PBF Finance Corp., 9.25%, 05/15/25(a)			2,721		2,778,005
Petroleos Mexicanos, 6.88%, 10/16/25			5,637		6,085,142
Pioneer Natural Resources Co., 1.90%, 08/15/30			4,765		4,422,222
Puma International Financing SA, 5.13%, 10/06/24(a)			4,115		4,113,714
Sabine Pass Liquefaction LLC
5.63%, 04/15/23			6,227		6,752,761
5.75%, 05/15/24			27,293		30,795,977
5.63%, 03/01/25			34,953		39,965,957
5.88%, 06/30/26			23,143		27,111,272
5.00%, 03/15/27			5,250		5,975,798
4.20%, 03/15/28			5,555		6,094,272
Shelf Drilling Holdings Ltd., 8.88%, 11/15/24(a)			436		444,901
SM Energy Co.
1.50%, 07/01/21(j)			5,224		5,172,324
10.00%, 01/15/25(a)			6,246		7,026,750
Suncor Energy, Inc.
6.80%, 05/15/38(n)			1,859		2,546,839
6.85%, 06/01/39			372		513,246

Security		Par (000)		Value
Oil, Gas & Consumable Fuels (continued)
Sunoco Logistics Partners Operations LP
4.25%, 04/01/24	USD		13,232	$	14,335,145
5.95%, 12/01/25			2,980		3,469,974
6.10%, 02/15/42			2,093		2,356,967
Sunoco LP/Sunoco Finance Corp.
5.50%, 02/15/26			1,054		1,082,764
6.00%, 04/15/27			798		834,908
Talos Production, Inc., 12.00%, 01/15/26(a)			9,836		9,626,985
Targa Resources Partners LP/Targa Resources Partners Finance Corp.
5.88%, 04/15/26			2,941		3,078,859
5.38%, 02/01/27			1,690		1,752,640
6.50%, 07/15/27			3,372		3,664,285
5.00%, 01/15/28			448		466,480
6.88%, 01/15/29			2,717		2,993,319
5.50%, 03/01/30			597		626,850
Texas Eastern Transmission LP
3.50%, 01/15/28(a)			6,561		6,939,646
4.15%, 01/15/48(a)			920		930,640
Thaioil Treasury Center Co. Ltd., 3.75%, 06/18/50			2,470		2,183,144
TransCanada PipeLines Ltd.
4.63%, 03/01/34			2,441		2,755,024
5.85%, 03/15/36			1,026		1,298,628
Transcontinental Gas Pipe Line Co. LLC
7.85%, 02/01/26			20,169		25,526,163
4.00%, 03/15/28			8,042		8,928,809
4.60%, 03/15/48			3,414		3,876,356
3.95%, 05/15/50			5,137		5,251,179
Western Midstream Operating LP, (3 mo. LIBOR US + 1.85%), 2.33%, 01/13/23(d)			4,291		4,206,090
Williams Cos., Inc., Series A, 7.50%, 01/15/31			2,180		2,887,134
WPX Energy, Inc.
8.25%, 08/01/23			375		430,313
5.88%, 06/15/28			362		399,033
					599,843,536
Paper & Forest Products — 0.1%
Celulosa Arauco y Constitucion SA, 4.25%, 04/30/29(a)			1,802		1,958,864
Georgia-Pacific LLC
1.75%, 09/30/25(a)			3,780		3,845,868
0.95%, 05/15/26(a)			1,350		1,307,199
2.10%, 04/30/27(a)			2,870		2,917,981
7.75%, 11/15/29			1,275		1,794,033
2.30%, 04/30/30(a)			4,364		4,347,306
8.88%, 05/15/31			528		807,573
Inversiones CMPC SA, 4.38%, 05/15/23(a)			827		869,901
Suzano Austria GmbH, 3.75%, 01/15/31			800		825,920
					18,674,645
Pharmaceuticals — 0.6%
AstraZeneca PLC, 1.38%, 08/06/30			16,728		15,343,311
Bausch Health Americas, Inc.
9.25%, 04/01/26(a)			3,933		4,357,764
8.50%, 01/31/27(a)			4,589		5,090,922
Bausch Health Cos., Inc.
5.50%, 11/01/25(a)			4,757		4,887,247
9.00%, 12/15/25(a)			3,992		4,337,188
5.75%, 08/15/27(a)			1,865		2,007,206
7.00%, 01/15/28(a)			1,897		2,059,288
7.25%, 05/30/29(a)			1,961		2,188,966
Bayer AG, 1.13%, 01/06/30	EUR		4,100		4,937,234
Bristol-Myers Squibb Co., 4.25%, 10/26/49	USD		2,532		2,982,380

MASTER  PORTFOLIO   SCHEDULE   OF   INVESTMENTS 55

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Pharmaceuticals (continued)
Eli Lilly & Co., 1.70%, 11/01/49	EUR		3,400	$	4,341,505
Endo Luxembourg Finance Co. I Sarl/Endo U.S., Inc., 6.13%, 04/01/29(a)	USD		1,000		1,008,750
Horizon Therapeutics USA, Inc., 5.50%, 08/01/27(a)			358		382,165
Johnson & Johnson, 3.50%, 01/15/48			2,585		2,839,279
Luye Pharma Group Ltd., 1.50%, 07/09/24(j)			900		932,673
Merck & Co., Inc., 2.45%, 06/24/50			2,945		2,597,278
Pfizer, Inc.
3.45%, 03/15/29			8,145		8,939,322
2.63%, 04/01/30			10,083		10,466,538
1.70%, 05/28/30			5,339		5,159,369
Pharmacia LLC, 6.60%, 12/01/28			2,164		2,868,339
Shire Acquisitions Investments Ireland DAC
2.88%, 09/23/23			4,400		4,623,345
3.20%, 09/23/26			2,753		2,965,966
Sino Biopharmaceutical Ltd., 0.00%, 02/17/25(j)(m)	EUR		924		1,062,445
Takeda Pharmaceutical Co. Ltd.
5.00%, 11/26/28	USD		8,445		9,994,388
2.05%, 03/31/30			7,902		7,615,854
2.00%, 07/09/40	EUR		9,260		11,610,724
Wyeth LLC, 5.95%, 04/01/37	USD		1,813		2,522,438
					128,121,884
Real Estate Management & Development — 0.4%
Agile Group Holdings Ltd.
8.38%(l)			350		365,641
5.75%, 01/02/25			650		664,422
6.05%, 10/13/25			200		206,813
Arabian Centres Sukuk II Ltd., 5.63%, 10/07/26(a)			3,135		3,134,020
Arabian Centres Sukuk Ltd., 5.38%, 11/26/24			1,736		1,766,380
Arrow Bidco LLC, 9.50%, 03/15/24(a)			2,177		2,155,230
Central China Real Estate Ltd.
7.25%, 04/24/23			200		189,000
7.65%, 08/27/23			200		185,000
CFLD Cayman Investment Ltd.
6.90%, 01/13/23			650		240,297
8.60%, 04/08/24			319		117,930
China Aoyuan Group Ltd.
7.95%, 02/19/23			1,765		1,822,362
6.35%, 02/08/24			1,100		1,102,406
China Evergrande Group
9.50%, 04/11/22			200		192,125
11.50%, 01/22/23			400		376,250
10.00%, 04/11/23			400		367,500
7.50%, 06/28/23			400		345,625
12.00%, 01/22/24			900		833,906
10.50%, 04/11/24			200		178,063
China SCE Group Holdings Ltd.
7.25%, 04/19/23			1,000		1,029,062
7.38%, 04/09/24			636		654,086
CIFI Holdings Group Co. Ltd.
6.45%, 11/07/24			200		212,563
6.00%, 07/16/25			200		212,250
5.95%, 10/20/25			800		850,250
5.25%, 05/13/26			305		313,002
Country Garden Holdings Co. Ltd.
6.50%, 04/08/24			200		213,875
5.40%, 05/27/25			965		1,039,787
6.15%, 09/17/25			200		221,688
2.70%, 07/12/26			695		687,181

Security		Par (000)		Value
Real Estate Management & Development (continued)
Country Garden Holdings Co. Ltd.
3.30%, 01/12/31	USD		1,055	$	996,975
Emaar Sukuk Ltd., 3.64%, 09/15/26			594		604,209
Esic Sukuk Ltd., 3.94%, 07/30/24			1,500		1,559,062
Fantasia Holdings Group Co. Ltd.
6.95%, 12/17/21			465		461,254
11.75%, 04/17/22			230		234,416
7.95%, 07/05/22			530		512,941
12.25%, 10/18/22			200		203,438
10.88%, 01/09/23			200		199,188
9.88%, 10/19/23			700		646,625
Five Point Operating Co. LP/Five Point Capital Corp., 7.88%, 11/15/25(a)			4,330		4,525,391
Forestar Group, Inc.
8.00%, 04/15/24(a)			9,456		9,869,700
5.00%, 03/01/28(a)			3,502		3,634,411
Gemdale Ever Prosperity Investment Ltd., 5.60%, 06/14/22			200		205,250
Global Prime Capital Pte Ltd., 5.95%, 01/23/25			451		466,785
Greenland Global Investment Ltd., 5.60%, 11/13/22			200		177,625
Hopson Development Holdings Ltd., 7.50%, 06/27/22			653		666,672
Howard Hughes Corp., 5.38%, 08/01/28(a)			4,396		4,621,295
Jingrui Holdings Ltd., 9.45%, 04/23/21			700		692,562
Kaisa Group Holdings Ltd.
11.95%, 10/22/22			900		944,156
11.50%, 01/30/23			200		206,688
10.88%, 07/23/23			790		820,119
11.95%, 11/12/23			215		225,817
9.38%, 06/30/24			2,206		2,120,517
KWG Group Holdings Ltd.
7.88%, 09/01/23			486		501,188
7.40%, 03/05/24			200		209,688
5.95%, 08/10/25			614		604,790
Logan Group Co. Ltd.
5.75%, 01/14/25			436		457,664
5.25%, 10/19/25			455		471,494
Logan Property Holdings Co. Ltd., 6.50%, 07/16/23			200		205,000
Longfor Group Holdings Ltd., 3.95%, 09/16/29			620		649,256
MAF Global Securities Ltd., 4.75%, 05/07/24			1,073		1,166,552
New Metro Global Ltd.
6.80%, 08/05/23			400		419,750
4.80%, 12/15/24			335		337,513
NWD MTN Ltd., 4.13%, 07/18/29			1,200		1,227,000
Powerlong Real Estate Holdings Ltd.
7.13%, 11/08/22			620		646,156
6.95%, 07/23/23			200		208,438
Realogy Group LLC/Realogy Co-Issuer Corp., 9.38%, 04/01/27(a)			410		454,068
Redsun Properties Group Ltd., 10.50%, 10/03/22			600		630,000
RKPF Overseas 2019 A Ltd., 6.00%, 09/04/25			595		617,127
RKPF Overseas 2020 A Ltd., 5.20%, 01/12/26			480		485,250
Ronshine China Holdings Ltd.
11.25%, 08/22/21			265		268,313
5.50%, 02/01/22			1,050		1,036,871
8.75%, 10/25/22			730		730,912
7.35%, 12/15/23			466		440,661
Scenery Journey Ltd.
11.50%, 10/24/22			665		608,059

56 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Real Estate Management & Development (continued)
Scenery Journey Ltd.
12.00%, 10/24/23	USD		800	$	705,000
Seazen Group Ltd.
6.45%, 06/11/22			200		205,438
6.00%, 08/12/24			400		422,000
Shimao Group Holdings Ltd.
5.60%, 07/15/26			200		216,125
4.60%, 07/13/30			1,263		1,329,307
3.45%, 01/11/31			200		190,188
Shui On Development Holding Ltd.
5.75%, 11/12/23			300		308,156
6.15%, 08/24/24			580		603,744
Sunac China Holdings Ltd.
8.35%, 04/19/23			200		208,250
7.95%, 10/11/23			200		211,250
7.50%, 02/01/24			200		210,438
6.65%, 08/03/24			700		717,937
7.00%, 07/09/25			302		309,456
Theta Capital Pte Ltd., 8.13%, 01/22/25			300		306,469
Times China Holdings Ltd.
5.75%, 04/26/22			500		505,010
6.75%, 07/16/23			295		306,431
6.75%, 07/08/25			500		524,687
Vanke Real Estate Hong Kong Co. Ltd., 3.15%, 05/12/25			1,650		1,708,266
Wanda Group Overseas Ltd., 7.50%, 07/24/22			840		750,487
Wheelock MTN BVI Ltd., 2.38%, 01/25/26			1,395		1,393,428
Yango Justice International Ltd.
9.25%, 04/15/23			600		605,437
8.25%, 11/25/23			400		394,375
Yanlord Land HK Co. Ltd.
6.75%, 04/23/23			200		207,625
6.80%, 02/27/24			680		713,787
Yuzhou Group Holdings Co. Ltd.
7.38%, 01/13/26			1,281		1,088,850
6.35%, 01/13/27			600		499,200
Yuzhou Properties Co. Ltd.
8.50%, 02/04/23			200		189,100
6.00%, 10/25/23			620		549,940
8.50%, 02/26/24			900		812,250
8.38%, 10/30/24			200		179,500
Zhenro Properties Group Ltd.
9.15%, 05/06/23			910		952,656
8.30%, 09/15/23			200		205,875
					84,178,222
Road & Rail — 0.6%
Burlington Northern Santa Fe LLC
5.75%, 05/01/40			4,135		5,534,840
5.05%, 03/01/41			9		11,303
4.40%, 03/15/42			2,921		3,414,602
3.30%, 09/15/51			11,000		11,033,311
CMB International Leasing Management Ltd.
2.00%, 02/04/26			570		562,485
2.75%, 08/12/30			1,150		1,102,203
CSX Corp.
4.25%, 03/15/29			4,955		5,627,506
2.40%, 02/15/30			2,541		2,555,076
5.50%, 04/15/41			285		368,880
4.30%, 03/01/48			5,959		6,792,430
4.75%, 11/15/48			379		455,551
3.35%, 09/15/49			2,236		2,194,668
4.25%, 11/01/66			3,597		4,086,797

Security		Par (000)		Value
Road & Rail (continued)
Norfolk Southern Corp.
3.65%, 08/01/25	USD		3,515	$	3,846,071
2.90%, 06/15/26			6,045		6,475,492
3.40%, 11/01/49			1,244		1,236,699
4.05%, 08/15/52			6,058		6,679,029
3.16%, 05/15/55			2,229		2,071,990
Penske Truck Leasing Co. LP/PTL Finance Corp.
4.25%, 01/17/23(a)			2,565		2,725,119
2.70%, 03/14/23(a)			3,425		3,552,162
2.70%, 11/01/24(a)			1,580		1,663,415
3.95%, 03/10/25(a)			2,210		2,412,619
4.00%, 07/15/25(a)			6,435		7,064,119
1.20%, 11/15/25(a)			4,536		4,455,613
4.45%, 01/29/26(a)			280		313,643
3.35%, 11/01/29(a)			930		963,190
Ryder System, Inc.
2.50%, 09/01/22			120		123,110
2.50%, 09/01/24			1,829		1,916,432
4.63%, 06/01/25			17,920		20,194,206
Union Pacific Corp.
3.25%, 08/15/25			4,144		4,479,884
2.75%, 03/01/26			4,737		5,017,342
3.84%, 03/20/60			10,971		11,659,945
Union Pacific Railroad Co. Pass-Through Trust, Series 2014-1, 3.23%, 05/14/26			2,583		2,795,694
					133,385,426
Semiconductors & Semiconductor Equipment — 1.1%
Applied Materials, Inc., 2.75%, 06/01/50			4,918		4,563,824
Broadcom Corp./Broadcom Cayman Finance Ltd., 3.88%, 01/15/27			10,184		11,058,857
Broadcom, Inc.
4.75%, 04/15/29			5,075		5,706,224
5.00%, 04/15/30			8,193		9,337,696
4.30%, 11/15/32			8,907		9,697,376
2.60%, 02/15/33(a)			5,563		5,182,134
3.42%, 04/15/33(a)			21,345		21,406,127
3.47%, 04/15/34(a)			32,731		32,842,914
Intel Corp.
3.73%, 12/08/47			9,559		10,296,877
4.75%, 03/25/50			2,412		3,023,424
KLA Corp.
4.10%, 03/15/29			9,367		10,530,743
5.00%, 03/15/49			980		1,232,863
3.30%, 03/01/50			11,466		11,012,985
Lam Research Corp.
3.75%, 03/15/26			7,638		8,465,931
4.88%, 03/15/49			4,318		5,563,849
2.88%, 06/15/50			5,283		5,035,974
3.13%, 06/15/60			276		266,394
Microchip Technology, Inc., 4.25%, 09/01/25(a)			2,000		2,089,495
NVIDIA Corp.
3.20%, 09/16/26			6,970		7,603,218
2.85%, 04/01/30			4,073		4,277,466
3.50%, 04/01/50			6,241		6,591,778
NXP BV/NXP Funding LLC/NXP USA, Inc.
4.30%, 06/18/29(a)(e)			16,413		18,356,774
3.40%, 05/01/30(a)			15,918		16,808,656
QUALCOMM, Inc.
4.80%, 05/20/45			3,650		4,584,811

MASTER  PORTFOLIO   SCHEDULE   OF   INVESTMENTS 57

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Semiconductors & Semiconductor Equipment (continued)
QUALCOMM, Inc.
4.30%, 05/20/47	USD		7,139	$	8,404,351
Rohm Co. Ltd., 0.00%, 12/05/24(j)(m)	JPY		30,000		305,993
					224,246,734
Software — 0.8%
Activision Blizzard, Inc.
1.35%, 09/15/30	USD		9,570		8,645,429
2.50%, 09/15/50			4,950		4,153,940
Autodesk, Inc., 3.50%, 06/15/27			15,336		16,769,950
Citrix Systems, Inc.
4.50%, 12/01/27			9,909		11,284,336
3.30%, 03/01/30			6,500		6,685,474
LogMeIn, Inc., 5.50%, 09/01/27(a)			1,000		1,046,880
Microsoft Corp., 2.92%, 03/17/52			19,992		19,693,167
Oracle Corp.
3.90%, 05/15/35			11,460		12,386,157
3.85%, 07/15/36			3,179		3,380,955
3.80%, 11/15/37			8,118		8,431,337
6.13%, 07/08/39			1,363		1,810,968
3.60%, 04/01/40			7,911		7,945,166
3.65%, 03/25/41			20,220		20,461,283
4.00%, 07/15/46			3,762		3,872,948
4.00%, 11/15/47			6,020		6,216,862
3.60%, 04/01/50			15,904		15,404,326
4.10%, 03/25/61			8,956		9,268,037
Playtika Holding Corp., 4.25%, 03/15/29(a)			972		957,614
					158,414,829
Specialty Retail — 0.3%
Home Depot, Inc., 2.95%, 06/15/29			20,522		21,757,809
Lowe’s Cos., Inc.
4.00%, 04/15/25			16,948		18,750,528
3.65%, 04/05/29			9,190		10,059,336
2.63%, 04/01/31			2,500		2,507,120
Zhongsheng Group Holdings Ltd., 3.00%, 01/13/26			645		648,338
					53,723,131
Technology Hardware, Storage & Peripherals — 0.4%
Apple Inc.
3.85%, 05/04/43			9,525		10,772,832
4.65%, 02/23/46			3,093		3,845,851
3.85%, 08/04/46			3,833		4,297,054
2.55%, 08/20/60			6,900		5,937,144
2.80%, 02/08/61			4,620		4,149,235
Dell International LLC/EMC Corp.
4.90%, 10/01/26(a)			9,113		10,338,633
8.35%, 07/15/46(a)			3,740		5,690,010
Hewlett Packard Enterprise Co., 4.65%, 10/01/24			20,404		22,777,052
HP, Inc., 6.00%, 09/15/41			285		359,035
NCR Corp., 8.13%, 04/15/25(a)			850		930,750
Radiate Holdco LLC/Radiate Finance, Inc., 4.50%, 09/15/26(a)			1,000		1,011,250
Seagate HDD Cayman , 4.09%, 06/01/29(a)			3,217		3,278,203
Xerox Holdings Corp., 5.00%, 08/15/25(a)			4,000		4,174,600
Xiaomi Best Time International Ltd., 0.00%, 12/17/27(j)(m)			300		318,750
					77,880,399
Textiles, Apparel & Luxury Goods — 0.0%
Hanesbrands, Inc.
4.63%, 05/15/24(a)			3,828		4,061,144
4.88%, 05/15/26(a)			537		575,933

Security		Par (000)		Value
Textiles, Apparel & Luxury Goods (continued)
Under Armour, Inc., 3.25%, 06/15/26	USD		358	$	358,215
William Carter Co., 5.63%, 03/15/27(a)			1,700		1,795,625
					6,790,917
Tobacco — 0.6%
Altria Group, Inc.
4.40%, 02/14/26			5,556		6,265,212
2.20%, 06/15/27	EUR		4,340		5,491,030
3.40%, 05/06/30	USD		2,630		2,751,603
3.13%, 06/15/31	EUR		12,780		17,252,588
2.45%, 02/04/32	USD		11,978		11,443,541
5.80%, 02/14/39			12,505		15,259,590
6.20%, 02/14/59			796		969,632
BAT Capital Corp.
3.22%, 08/15/24			10,667		11,364,234
3.22%, 09/06/26			6,146		6,491,295
4.91%, 04/02/30			8,747		9,987,235
2.73%, 03/25/31			13,914		13,456,589
Philip Morris International, Inc., 1.45%, 08/01/39	EUR		10,050		11,240,408
Reynolds American, Inc.
4.45%, 06/12/25	USD		9,839		10,917,742
5.85%, 08/15/45			6,970		8,215,713
					131,106,412
Trading Companies & Distributors — 0.1%
American Builders & Contractors Supply Co., Inc.
5.88%, 05/15/26(a)			1,723		1,779,308
4.00%, 01/15/28(a)			2,286		2,286,000
Beacon Roofing Supply, Inc., 4.88%, 11/01/25(a)			3,424		3,501,040
Herc Holdings, Inc., 5.50%, 07/15/27(a)			3,403		3,621,473
United Rentals North America, Inc.
5.88%, 09/15/26			3,421		3,579,221
5.50%, 05/15/27			3,428		3,655,962
3.88%, 11/15/27			4,513		4,676,596
4.88%, 01/15/28			7,036		7,411,511
5.25%, 01/15/30			448		486,215
					30,997,326
Transportation Infrastructure — 0.0%
Delhi International Airport Ltd., 6.13%, 10/31/26			300		305,906
ENA Master Trust, 4.00%, 05/19/48(a)			1,460		1,472,775
Rumo Luxembourg S.a.r.l, 5.88%, 01/18/25(a)			728		764,400
					2,543,081
Wireless Telecommunication Services — 0.6%
Bharti Airtel Ltd., 3.25%, 06/03/31			1,055		1,027,232
Digicel Group 0.5 Ltd., (5.00% Cash and 3.00% PIK or 8.00% PIK), 8.00%, 04/01/25(a)(i)			1,012		824,981
Digicel Ltd., 6.75%, 03/01/23(a)			233		210,792
Kenbourne Invest SA
6.88%, 11/26/24(a)			3,075		3,271,031
4.70%, 01/22/28(a)			1,260		1,285,200
Millicom International Cellular SA
6.63%, 10/15/26(a)			990		1,052,803
4.50%, 04/27/31(a)			2,825		2,938,000
Sprint Corp.
7.88%, 09/15/23			3,312		3,785,616
7.13%, 06/15/24			2,156		2,482,095
7.63%, 02/15/25			4,480		5,342,400
7.63%, 03/01/26			4,516		5,530,745

58 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Wireless Telecommunication Services (continued)
Sprint Spectrum Co. LLC/Sprint Spectrum Co. II LLC/Sprint Spectrum Co. III LLC, 3.36%, 09/20/21(a)	USD		2,064	$	2,079,858
T-Mobile USA, Inc.
3.75%, 04/15/27(a)			17,819		19,479,018
3.88%, 04/15/30(a)			48,540		52,683,375
Vodafone Group PLC, 5.25%, 05/30/48			18,716		23,365,780
					125,358,926
Total Corporate Bonds — 37.4% (Cost: $7,786,192,471)					7,874,374,404
Floating Rate Loan Interests(d)
Air Freight & Logistics — 0.0%
XPO Logistics, Inc., Refinancing Term Loan (2018), (3 mo. LIBOR US + 1.75%, 0.00% Floor), 2.12%, 02/23/25			6,661		6,613,722
Airlines — 0.1%
Allegiant Travel Co., Replacement Term Loan, (3 mo. LIBOR US + 3.00%, 0.00% Floor), 3.21%, 02/05/24			11,927		11,811,893
Kestrel Bidco, Inc. (AKAWestJet Airlines), Term Loan, (3 mo. LIBOR US + 3.00%, 1.00% Floor), 4.00%, 12/11/26			14,582		14,131,233
					25,943,126
Beverages — 0.0%
City Brewing Co. LLC, Term Loan B, 4.25%, 03/31/28(o)			2,169		2,163,577
Triton Water Holdings, Inc., Term Loan, 4.00%, 03/31/28(o)			2,299		2,288,218
					4,451,795
Biotechnology — 0.0%
Grifols Worldwide Operations Ltd., Dollar Tranche B Term Loan, (1 wk. LIBOR US + 2.00%, 0.00% Floor), 2.08%, 11/15/27			7,167		7,083,085
Building Products — 0.0%
JELD-WEN, Inc., Term B-4 Loan, (1 mo. LIBOR US + 2.00%, 0.00% Floor), 2.18%, 12/14/24			2,875		2,857,029
TAMKO Building Products LLC
Initial Term Loan, (1 mo. LIBOR US + 3.00%, 0.00% Floor), 3.11%, 05/31/26			2,788		2,771,921
Initial Term Loan, (2 mo. LIBOR US + 3.00%, 0.00% Floor), 3.36%, 05/31/26			958		952,981
					6,581,931
Commercial Services & Supplies — 0.1%
621 17th Street Operating Co. LLC (633 17th Street Operating Co. LLC), Loan, (1 mo. LIBOR US + 2.90%, 0.00% Floor), 2.90%, 05/15/21(b)			8,600		7,912,000
KAR Auction Services, Inc., Tranche B-6 Term Loan, (1 mo. LIBOR US + 2.25%, 0.00% Floor), 2.38%, 09/19/26			1,064		1,041,323
Signal Parent, Inc., Cov-Lite Term Loan B, 4.25%, 04/01/28(b)(o)			3,445		3,419,163
					12,372,486

Security		Par (000)		Value
Construction & Engineering — 0.0%
PLH Infrastructure Services, Inc., Term Loan, (3 mo. LIBOR US + 6.00%, 0.00% Floor), 7.00%, 08/07/23(b)	USD		2,447	$	2,300,338
Ply Gem Midco, Inc., Initial Term Loan, (1 mo. LIBOR US + 3.75%, 0.00% Floor), 3.86%, 04/12/25			2,323		2,319,198
					4,619,536
Construction Materials — 0.1%
Advanced Drainage Systems, Inc., Initial Term Loan, (1 mo. LIBOR US + 2.25%, 0.00% Floor), 2.44%, 09/24/26			751		751,386
White Cap Buyer LLC, Initial Closing Date Term Loan, (3 mo. LIBOR US + 4.00%, 0.50% Floor), 4.50%, 10/19/27			8,163		8,142,136
					8,893,522
Consumer Finance — 0.0%
Crédito Real SAB de CV, SOFOM, ENR (Marevalley Corp.), Tranche A Loan, (3 mo. LIBOR US + 3.75%, 0.00% Floor), 3.75%, 02/21/23(b)			815		797,070
Distributors — 0.1%
Amazon Logistics, Term Loan, (1 mo. LIBOR US + 2.95%, 0.25% Floor), 3.50%, 10/09/23			19,797		19,796,924
Diversified Financial Services — 0.3%
18 Fremont Street Acquisition LLC, Term Loan, (3 mo. LIBOR US + 8.00%, 1.50% Floor), 10.03%, 08/09/25			12,000		12,120,276
BSREP II Houston Office 1HC Owner LLC, Mezzanine Loan, (1 mo. LIBOR US + 2.10%, 0.00% Floor), 1.81%, 01/09/22(b)			10,970		10,943,472
Flutter Entertainment PLC, USD Term Loan, (3 mo. LIBOR US + 3.50%, 0.00% Floor), 3.75%, 07/10/25			2,684		2,685,562
Intelsat Jackson Holdings SA
DIP Facility, (3 mo. LIBOR US + 5.50%, 1.00% Floor), 6.25%, 07/13/21			2,579		2,606,059
Tranche B-3 Term Loan, (1 mo. PRIME US + 4.75%, 1.00% Floor), 3.25%, 11/27/23			1,275		1,294,125
Tranche B-4 Term Loan, (1 mo. PRIME US + 5.50%, 1.00% Floor), 8.75%, 01/02/24			1,458		1,486,708
PECO-PD III Borrower LP, Revolving Loan, 2.15%, 11/30/24			14,481		14,481,257
RNTR-1 LLC (AKA Seer Sylvan), Initial Term Loan, (1 mo. LIBOR US + 2.38%, 0.25% Floor), 2.66%, 12/20/21(b)			7,253		7,234,413
Woof Holdings, Inc., Initial Term Loan (First Lien), (1 yr. LIBOR US + 3.75%, 0.75% Floor), 4.50%, 12/21/27			1,888		1,878,560
					54,730,432
Diversified Telecommunication Services — 0.0%
Cablevision Lightpath LLC, Initial Term Loan, (1 mo. LIBOR US + 3.25%, 0.50% Floor), 3.75%, 12/01/27			1,220		1,216,892
Connect Finco S.a.r.l (AKA Inmarsat), Amendment No. 1 Refinancing Term Loan, (1 mo. LIBOR US + 3.50%, 1.00% Floor), 4.50%, 12/12/26			2,510		2,499,185
					3,716,077

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 59

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Electronic Equipment, Instruments & Components — 0.0%
Robertshaw U.S. Holding Corp. (FKA Fox U.S. Bidco Corp.), Initial Term Loan (Second Lien), (1 mo. LIBOR US + 8.00%, 1.00% Floor), 10.13%, 02/28/26	USD		1,795	$	1,537,723
Equity Real Estate Investment Trusts (REITs) — 0.1%
VICI Properties 1 LLC, Term B Loan, (1 mo. LIBOR US + 1.75%, 0.00% Floor), 3.65%, 12/22/24			8,361		8,260,699
Food Products — 0.0%
JBS USA Lux SA (FKA JBS USA LLC), New Term Loan, (1 mo. LIBOR US + 2.00%, 0.00% Floor), 4.54%, 05/01/26			3,325		3,302,042
Shearer’s Foods LLC, Refinancing Term Loan (First Lien), (3 mo. LIBOR US + 3.50%, 0.75% Floor), 0.00%, 09/30/25			987		984,421
					4,286,463
Health Care Providers & Services — 0.0%
Gentiva Health Services, Inc., Term B-1 Loan (First Lien), (1 mo. LIBOR US + 2.75%, 0.00% Floor), 2.88%, 07/02/25			3,456		3,431,154
Select Medical Corp., Tranche B Term Loan, (1 mo. LIBOR US + 2.25%, 0.00% Floor), 2.53%, 03/06/25			1,124		1,116,079
					4,547,233
Hotels, Restaurants & Leisure — 0.3%
Aimbridge Acquisition Co., Inc.
2020 Incremental Term Loan (First Lien), (1 mo. LIBOR US + 6.00%, 0.75% Floor), 6.75%, 02/01/26(b)			2,042		2,041,740
Initial Term Loan (2019) (First Lien), (1 mo. LIBOR US + 3.75%, 0.00% Floor), 3.93%, 02/01/26(b)			3,894		3,777,034
Caesars Resort Collection LLC, Term B-1 Loan, (1 mo. LIBOR US + 4.50%, 0.00% Floor), 4.62%, 07/20/25			2,192		2,194,725
DuPont Hotel Project Owner LLC, Term Loan, (1 mo. LIBOR US + 2.50%, 1.00% Floor), 4.91%, 04/01/24(b)			12,071		11,105,570
ECL Entertainment LLC, Term Loan, 8.25%, 03/31/28(o)			5,278		5,278,000
Enterprise Development Authority, Term Loan B, 5.00%, 02/01/28(b)(o)			3,595		3,603,988
Golden Nugget, Inc. (AKA Landry’s, Inc.), Initial B Term Loan, (2 mo. LIBOR US + 2.50%, 0.75% Floor), 4.14%, 10/04/23			6,476		6,367,175
Herschend Entertainment Company LLC, Initial Term Loan, (3 mo. LIBOR US + 5.75%, 1.00% Floor), 6.75%, 08/25/25(b)			5,436		5,517,220
PCI Gaming Authority, Term B Facility Loan, (1 mo. LIBOR US + 2.50%, 0.00% Floor), 5.04%, 05/31/26			6,597		6,544,764
Spectacle Gary Holdings LLC
Closing Date Term Loan, (3 mo. LIBOR US + 9.00%, 2.00% Floor), 11.00%, 12/23/25			13,889		15,138,553
Delayed Draw Term Loan, (3 mo. LIBOR US + 9.00%, 2.00% Floor), 11.00%, 12/23/25			1,006		1,096,997
					62,665,766

Security		Par (000)		Value
Household Durables — 0.0%
MI Windows and Doors LLC, Initial Term Loan, (1 mo. LIBOR US + 3.75%, 0.75% Floor), 4.50%, 12/18/27	USD		3,152	$	3,161,966
Independent Power and Renewable Electricity Producers — 0.0%
WIN Waste Innovations Holdings, Inc., Initial Term Loan, 3.25%, 03/25/28(o)			800		797,000
IT Services — 0.1%
Avaya, Inc.
Tranche B-1 Term Loan, (1 mo. LIBOR US + 4.25%, 0.00% Floor), 4.36%, 12/15/27			1,000		999,840
Tranche B-2 Term Loan, 4.11%, 12/15/27(o)			1,000		999,290
Dun & Bradstreet Corp., Initial Term Borrowing, (1 mo. LIBOR US + 3.25%, 0.00% Floor), 3.89%, 02/08/26			1,995		1,982,531
LogMeIn, Inc., Initial Term Loan (First Lien), (1 mo. LIBOR US + 4.75%, 0.00% Floor), 4.85%, 08/31/27			3,705		3,691,971
Peraton Corp.
Additional Term Loan, 4.75%, 02/01/28(o)			840		839,145
Term B Loan (First Lien), 4.50%, 02/01/28(o)			477		476,812
Term Loan B1 (Second Lien), 7.68%, 02/26/29(b)(o)			406		412,090
RealPage, Inc., Term Loan, 3.75%, 02/18/28(o)			1,000		994,860
Surf Holdings S.a r.l (AKA Sophos), Dollar Tranche Term Loan (First Lien), 3.68%, 03/05/27(o)			2,052		2,030,644
					12,427,183
Machinery — 0.0%
Douglas Dynamics LLC, 2020 Term B Loan, (1 mo. LIBOR US + 3.75%, 1.00% Floor), 4.75%, 06/08/26			1,047		1,041,068
Gates Global LLC, Initial B-3 Dollar Term Loan, (1 mo. LIBOR US + 2.75%, 0.75% Floor), 3.50%, 03/31/27			800		796,918
					1,837,986
Media — 0.1%
Burlingame Point LLC, Construction Loan, 2.03%, 05/09/23(b)(o)			10,414		10,414,166
Charter Communications Operating LLC (AKA CCO Safari LLC), Term A-4 Loan, (1 mo. LIBOR US + 1.25%, 0.00% Floor), 1.25%, 02/01/25(b)			4,125		4,104,417
CSC Holdings LLC (FKA CSC Holdings, Inc. (Cablevision)), September 2019 Initial Term Loan, (1 mo. LIBOR US + 2.50%, 0.00% Floor), 1.00%, 04/15/27			4,503		4,443,934
Lamar Media Corp., Term B Loan, (1 mo. LIBOR US + 1.50%, 0.00% Floor), 1.60%, 02/06/27			477		472,848
					19,435,365
Metals & Mining — 0.0%
Zekelman Industries, Inc. (FKA JMC Steel Group, Inc.), 2020 Term Loan, (1 mo. LIBOR US + 2.00%, 0.00% Floor), 2.11%, 01/24/27			1,335		1,316,461
Multi-Utilities — 0.0%
PG&E Corp., Loan, (3 mo. LIBOR US + 3.00%, 0.50% Floor), 5.50%, 01/01/22			7,741		7,723,556

60 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Oil, Gas & Consumable Fuels — 0.1%
BCP Raptor II LLC, Initial Term Loan, (1 mo. LIBOR US + 4.75%, 0.00% Floor), 4.86%, 11/03/25	USD		9,379	$	8,921,978
Buckeye Partners LP, 2021 Tranche B-1 Term Loan, (1 mo. LIBOR US + 2.25%, 0.00% Floor), 2.37%, 11/01/26			11,520		11,459,840
					20,381,818
Real Estate Management & Development — 0.1%
BRE Park Avenue Tower Owner LLC, Mezzanine A Loan, (1 mo. LIBOR US + 2.05%, 0.00% Floor), 2.16%, 03/09/24(b)			16,472		16,470,289
Road & Rail — 0.0%
Genesee & Wyoming, Inc., Initial Term Loan, (3 mo. LIBOR US + 2.00%, 0.00% Floor), 2.25%, 12/30/26			4,215		4,198,305
Software — 0.1%
Applied Systems, Inc.
Closing Date Term Loan (First Lien), (3 mo. LIBOR US + 3.00%, 0.50% Floor), 4.25%, 09/19/24			492		489,932
Closing Date Term Loan (First Lien), (3 mo. PRIME US + 2.00%, 0.50% Floor), 5.25%, 09/19/24			7		6,823
athenahealth, Inc., Term B-1 Loan (First Lien), (3 mo. LIBOR US + 4.25%, 0.00% Floor), 4.45%, 02/11/26			844		844,700
Barracuda Networks, Inc., 2020 Term Loan (First Lien), 4.50%, 02/12/25(o)			2,000		1,997,000
Informatica LLC (FKA Informatica Corp.), Dollar 2020 Term Loan, 3.37%, 02/14/27(o)			1,995		1,978,005
Interface Security Systems LLC, Initial Term Loan, (3 mo. LIBOR US + 7.00%, 1.75% Floor), 9.18%, 08/07/23(b)			5,372		5,392,442
Playtika Holding Corp., Term B-1 Loan, 2.75%, 03/11/28(o)			6,508		6,467,325
Project Ruby Ultimate Parent Corp. (Mediware), Closing Date Term Loan (First Lien), (3 mo. LIBOR US + 3.25%, 0.75% Floor), 4.00%, 03/10/28			2,378		2,367,109
					19,543,336
Specialty Retail — 0.0%
Foundation Building Materials, Inc.
Initial Term Loan (First Lien), (1 mo. LIBOR US + 3.25%, 0.50% Floor), 4.75%, 01/29/28			644		637,771
Term Loan, 3.75%, 01/29/28			373		368,832
LBM Acquisition LLC
Initial Delayed Draw Term Loan (First Lien), 4.50%, 12/17/27(o)			337		335,519
Initial Term Loan (First Lien), (3 mo. LIBOR US + 3.75%, 0.75% Floor), 4.50%, 12/17/27			1,517		1,509,837
Park River Holdings, Inc., Initial Term Loan (First Lien), (2 mo. LIBOR US + 3.25%, 0.75% Floor), 4.00%, 12/28/27			1,223		1,214,598
					4,066,557

Security		Par (000)		Value
Technology Hardware, Storage & Peripherals — 0.0%
Everi Payments, Inc.
Term B Loan, (1 mo. LIBOR US + 2.75%, 0.75% Floor), 4.70%, 05/09/24	USD		806	$	800,787
Term Loan, (1 mo. LIBOR US + 10.50%, 0.75% Floor), 11.50%, 05/09/24(b)			732		765,426
					1,566,213
Thrifts & Mortgage Finance — 0.1%
Caliber Home Loans, Inc.
Term Loan, (1 mo. LIBOR US + 3.00%, 0.00% Floor), 3.12%, 04/24/21(b)			5,595		5,578,215
Term Loan, (1 mo. LIBOR US + 3.25%, 0.00% Floor), 3.15%, 04/24/21(b)			3,764		3,752,617
					9,330,832
Total Floating Rate Loan Interests — 1.7% (Cost: $360,250,374)					359,154,457
Foreign Agency Obligations
Argentina — 0.0%
YPF SA, 7.00%, 12/15/47(a)			2,982		1,668,056
Bahrain — 0.0%
Oil and Gas Holding Co. BSCC, 7.63%, 11/07/24			2,309		2,569,484
Brazil — 0.1%
Banco do Brasil SA, 5.88%, 01/26/22(a)			1,244		1,287,929
Centrais Eletricas Brasileiras SA
5.75%, 10/27/21(a)			365		373,212
3.63%, 02/04/25(a)			1,830		1,840,866
Petrobras Global Finance BV
6.25%, 03/17/24			1,008		1,116,045
5.30%, 01/27/25			3,596		3,946,610
5.09%, 01/15/30			4,174		4,336,368
5.60%, 01/03/31			4,272		4,502,688
					17,403,718
Chile — 0.0%
Corp Nacional del Cobre de Chile, 3.75%, 01/15/31(a)			730		788,400
China — 0.1%
China Cinda 2020 I Management Ltd., 3.00%, 01/20/31			265		261,860
China Construction Bank Corp.
4.25%, 02/27/29			805		869,148
2.45%, 06/24/30			2,950		3,001,625
China Development Bank Financial Leasing Co. Ltd., 2.88%, 09/28/30			1,200		1,216,578
China Minmetals Corp., 3.75%(l)			339		345,674
China Resources Land Ltd., 3.75%(l)			1,450		1,502,563
Chinalco Capital Holdings Ltd.
4.10%, (l)			735		763,022
4.25%, 04/21/22			1,025		1,043,258
CITIC Ltd., 2.85%, 02/25/30			1,140		1,129,669
Huarong Finance 2019 Co. Ltd.
4.25%, (l)			332		341,960
3.25%, 11/13/24			2,300		2,377,757
4.50%, 05/29/29			1,300		1,370,281
3.88%, 11/13/29			1,600		1,618,000
3.63%, 09/30/30			1,240		1,224,500
Huarong Finance II Co. Ltd., 5.00%, 11/19/25			663		728,471
Leader Goal International Ltd., 4.25%(l)			700		719,031
Ocean Laurel Co. Ltd., 2.38%, 10/20/25			660		650,306

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 61

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
China (continued)
Rongshi International Finance Ltd., 3.75%, 05/21/29	USD		1,945	$	2,064,739
Sino-Ocean Land Treasure IV Ltd.
5.25%, 04/30/22			480		496,418
4.75%, 08/05/29			1,615		1,631,655
Sunny Express Enterprises Corp., 3.13%, 04/23/30			1,385		1,394,111
					24,750,626
Colombia — 0.1%
Ecopetrol SA
5.38%, 06/26/26			11,184		12,499,574
6.88%, 04/29/30			5,371		6,505,624
Empresas Publicas de Medellin ESP
4.25%, 07/18/29(a)			1,883		1,890,061
4.38%, 02/15/31(a)			1,447		1,449,894
Oleoducto Central SA, 4.00%, 07/14/27(a)			2,213		2,337,481
					24,682,634
Hong Kong — 0.0%
Nanyang Commercial Bank Ltd., 3.80%, 11/20/29			1,750		1,834,766
India — 0.0%
Bharat Petroleum Corp. Ltd., 4.00%, 05/08/25			473		495,024
Greenko Dutch BV
5.25%, 07/24/24			200		207,375
3.85%, 03/29/26			200		200,688
Greenko Investment Co., 4.88%, 08/16/23			200		203,187
Greenko Solar Mauritius Ltd., 5.55%, 01/29/25			200		205,000
Oil India Ltd., 5.13%, 02/04/29			880		975,938
Power Finance Corp. Ltd.
4.50%, 06/18/29			3,484		3,687,596
3.35%, 05/16/31			560		545,373
REC Ltd.
3.88%, 07/07/27			279		292,601
4.63%, 03/22/28			200		214,062
					7,026,844
Indonesia — 0.0%
Majapahit Holding BV, 7.88%, 06/29/37			650		892,735
Pertamina Persero PT, 4.18%, 01/21/50			942		913,151
Perusahaan Listrik Negara PT, 6.25%, 01/25/49			1,858		2,291,727
					4,097,613
Kazakhstan — 0.0%
KazMunayGas National Co. JSC, 3.50%, 04/14/33(a)			1,350		1,381,725
Kuwait — 0.1%
Equate Petrochemical BV, 4.25%, 11/03/26			879		957,561
MEGlobal Canada ULC
5.00%, 05/18/25(a)			3,035		3,373,592
5.00%, 05/18/25			3,400		3,779,312
5.88%, 05/18/30(a)			1,770		2,132,850
5.88%, 05/18/30			1,350		1,626,750
					11,870,065
Malaysia — 0.0%
Tenaga Nasional Bhd, 7.50%, 01/15/96			850		1,030,281
Mexico — 0.2%
Mexico City Airport Trust, 5.50%, 07/31/47			7,086		6,981,836
Petroleos Mexicanos
6.84%, 01/23/30			8,325		8,417,824
6.38%, 01/23/45			4,915		4,079,450
5.63%, 01/23/46			1,198		952,230

Security		Par (000)		Value
Mexico (continued)
Petroleos Mexicanos
6.35%, 02/12/48	USD		1,490	$	1,227,388
7.69%, 01/23/50			3,547		3,277,428
6.95%, 01/28/60			4,438		3,788,942
					28,725,098
Morocco — 0.0%
OCP SA, 4.50%, 10/22/25			1,171		1,236,503
Oman — 0.0%
Oryx Funding Ltd., 5.80%, 02/03/31(a)			1,365		1,411,069
Panama — 0.0%
Banco Latinoamericano de Comercio Exterior SA, 2.38%, 09/14/25(a)			2,301		2,335,515
Singapore — 0.0%
BOC Aviation Ltd., 3.00%, 09/11/29			2,000		1,986,250
South Africa — 0.0%
Eskom Holdings SOC Ltd., 7.13%, 02/11/25			1,424		1,470,280
United Arab Emirates — 0.1%
Abu Dhabi Crude Oil Pipeline LLC, 4.60%, 11/02/47			1,100		1,241,625
DAE Funding LLC, 2.63%, 03/20/25(a)			2,505		2,519,091
DP World Crescent Ltd., 3.91%, 05/31/23			2,019		2,123,887
ICD Funding Ltd., 3.22%, 04/28/26			750		759,141
MDGH - GMTN BV
2.50%, 11/07/24(a)			2,650		2,778,359
2.88%, 11/07/29(a)			1,779		1,840,709
					11,262,812
United States — 0.0%
Citgo Holding, Inc., 9.25%, 08/01/24(a)			1,775		1,761,688
Total Foreign Agency Obligations — 0.7% (Cost: $145,016,545)					149,293,427
Foreign Government Obligations
Argentina — 0.0%
Republic of Argentina, 0.13%, 07/09/35(c)			16,739		4,938,005
Bahrain — 0.0%
Kingdom of Bahrain
6.00%, 09/19/44			4,717		4,403,025
7.50%, 09/20/47			1,145		1,187,937
					5,590,962
Brazil — 0.1%
Federative Republic of Brazil, 3.88%, 06/12/30			32,720		31,717,465
China — 4.3%
People’s Republic of China 3.30%, 07/04/23	CNH		3,500		540,622
1.99%, 04/09/25	CNY		3,057,570		447,240,676
2.41%, 06/19/25			447,300		66,668,635
2.85%, 06/04/27			318,800		47,677,136
3.29%, 05/23/29			79,700		12,190,452
2.68%, 05/21/30			2,221,040		323,462,609
					897,780,130
Colombia — 0.4%
Republic of Colombia
3.88%, 04/25/27	USD		16,282		17,406,476
4.50%, 03/15/29			13,000		14,198,437

62 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Colombia (continued)
Republic of Colombia
3.13%, 04/15/31	USD		32,689	$	31,994,359
5.20%, 05/15/49			12,646		13,910,600
					77,509,872
Dominican Republic — 0.2%
Dominican Republic
4.50%, 01/30/30			26,316		26,439,356
4.88%, 09/23/32(a)			20,018		20,218,180
					46,657,536
Ecuador — 0.0%
Republic of Ecuador, 0.50%, 07/31/35(c)			1,394		637,755
Egypt — 0.1%
Arab Republic of Egypt
6.38%, 04/11/31(a)	EUR		1,657		1,994,172
7.63%, 05/29/32	USD		2,577		2,630,151
7.90%, 02/21/48			2,349		2,205,858
8.88%, 05/29/50(a)			4,205		4,291,728
					11,121,909
France — 0.1%
Republic of France
1.50%, 05/25/50(a)	EUR		4,186		5,856,587
0.50%, 05/25/72(a)			8,250		7,870,313
					13,726,900
Ghana — 0.0%
Republic of Ghana
8.63%, 04/07/34(a)	USD		2,947		2,880,692
8.88%, 05/07/42(a)			2,953		2,827,498
					5,708,190
Greece — 0.0%
Hellenic Republic, 1.88%, 01/24/52(a)	EUR		6,150		7,163,481
Hungary — 0.0%
Republic of Hungary, 5.38%, 03/25/24	USD		8,710		9,880,406
Indonesia — 0.2%
Perusahaan Penerbit SBSN Indonesia III, 3.80%, 06/23/50			1,504		1,519,510
Republic of Indonesia
4.10%, 04/24/28			10,993		12,157,571
2.85%, 02/14/30			8,000		8,145,000
6.50%, 02/15/31	IDR		101,330,000		6,850,846
7.50%, 06/15/35			76,108,000		5,358,521
4.63%, 04/15/43	USD		432		477,765
4.75%, 07/18/47			433		487,666
7.38%, 05/15/48	IDR		57,269,000		3,843,475
					38,840,354
Italy — 0.0%
Buoni Poliennali Del Tesoro, 0.15%, 05/15/51(a)	EUR		8,190		9,654,817
Japan — 0.1%
Japanese Government CPI Linked Bond, 0.10%, 03/10/28	JPY		2,391,275		21,764,973
Maldives — 0.0%
Republic of Maldives, 7.00%, 06/07/22	USD		775		707,914
Mexico — 0.5%
United Mexican States
2.66%, 05/24/31			81,853		77,632,455
4.50%, 01/31/50			23,504		23,746,385
					101,378,840

Security		Par (000)		Value
Mongolia — 0.0%
Mongolian People’s Republic, 8.75%, 03/09/24	USD		236	$	271,400
Pakistan — 0.0%
Islamic Republic of Pakistan
6.00%, 04/08/26			200		203,188
7.38%, 04/08/31			200		204,187
					407,375
Panama — 0.2%
Republic of Panama
3.88%, 03/17/28			25,538		27,836,420
3.16%, 01/23/30			3,013		3,131,637
2.25%, 09/29/32			6,025		5,706,805
					36,674,862
Peru — 0.1%
Republic of Peru, 4.13%, 08/25/27			17,494		19,560,479
Philippines — 0.2%
Republic of the Philippines, 3.00%, 02/01/28			30,655		32,446,172
Romania — 0.0%
Republic of Romania, 3.00%, 02/14/31(a)			5,070		5,074,753
Russian Federation — 0.1%
Russian Federation
7.75%, 09/16/26	RUB		1,136,777		15,777,009
7.65%, 04/10/30			764,750		10,598,276
8.50%, 09/17/31			113,705		1,671,363
					28,046,648
Sri Lanka — 0.0%
Republic of Sri Lanka
6.85%, 03/14/24	USD		625		398,242
6.35%, 06/28/24			200		127,688
7.85%, 03/14/29			200		122,250
7.55%, 03/28/30			1,200		732,000
					1,380,180
Ukraine — 0.1%
Ukraine Government
9.75%, 11/01/28			8,135		9,472,190
7.38%, 09/25/32			5,195		5,209,611
7.25%, 03/15/33			3,727		3,706,036
					18,387,837
Uruguay — 0.1%
Republic of Uruguay
4.38%, 10/27/27			9,858		11,195,392
5.10%, 06/18/50			3,180		3,934,256
					15,129,648
Total Foreign Government Obligations — 6.8% (Cost: $1,419,144,175)					1,442,158,863
Municipal Bonds
California — 0.3%
Bay Area Toll Authority, RB, Series S1, 7.04%, 04/01/50			6,910		11,382,843
Los Angeles Community College District, GO, 6.60%, 08/01/42			3,990		6,255,282
Los Angeles Unified School District
GO, 5.75%, 07/01/34			415		548,240
GO, 6.76%, 07/01/34			7,405		10,466,820
State of California GO, 7.55%, 04/01/39			3,400		5,508,340

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 63

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
California (continued)
State of California Refunding GO, 4.60%, 04/01/38	USD		22,215	$	25,472,164
University of California, RB, 4.86%, 05/15/2112			1,940		2,440,772
					62,074,461
Georgia — 0.0%
Municipal Electric Authority of Georgia, RB, 6.64%, 04/01/57			2,487		3,564,692
Illinois — 0.1%
State of Illinois, GO, 5.10%, 06/01/33			13,140		14,788,413
Massachusetts — 0.0%
Massachusetts HFA, RB, Series A, 4.50%, 12/01/48			1,160		1,241,177
New Jersey — 0.0%
New Jersey Turnpike Authority, RB, Series F, 7.41%, 01/01/40			2,329		3,666,405
NewYork — 0.1%
Metropolitan Transportation Authority
RB, 5.87%, 11/15/39			735		918,993
RB, 6.67%, 11/15/39			350		473,994
RB, Series E, 6.81%, 11/15/40			860		1,176,291
New York City Water & Sewer System
RB, 6.01%, 06/15/42			665		964,616
RB, 5.88%, 06/15/44			1,240		1,800,629
New York State Dormitory Authority, RB, Series H, 5.39%, 03/15/40			1,470		1,882,673
Port Authority of New York & New Jersey
RB, 5.65%, 11/01/40			2,165		2,926,062
RB, 4.96%, 08/01/46			5,020		6,420,630
RB, 4.93%, 10/01/51			1,045		1,365,658
					17,929,546
Ohio — 0.0%
American Municipal Power, Inc., RB, Series B, 8.08%, 02/15/50			2,650		4,622,527
Puerto Rico — 0.1%
Puerto Rico Sales Tax Financing Corp. Sales Tax Revenue
RB, Series A-1, 0.00%, 07/01/46(m)			41,207		12,581,322
RB, Series A-1, 0.00%, 07/01/51(m)			25,029		5,535,914
					18,117,236
Texas — 0.0%
City of San Antonio, TX Electric & Gas Systems Revenue, RB, 5.81%, 02/01/41			3,260		4,547,439
State of Texas, GO, 5.52%, 04/01/39			4,260		6,049,669
					10,597,108
Total Municipal Bonds — 0.6% (Cost: $120,199,312)					136,601,565
Non-Agency Mortgage-Backed Securities
Collateralized Mortgage Obligations — 2.1%
1Texas Capital Bank CLN, Series M, 0.00%, 02/01/26(b)			18,500		18,500,000
Alternative Loan Trust, Series 2007-14T2, Class A1, 6.00%, 07/25/37			2,472		1,701,689
American Home Mortgage Assets Trust Series 2006-3, Class 2A11, (12 mo. Federal Reserve Cumulative Average US + 0.94%), 1.20%, 10/25/46(d)			792		653,550

Security		Par (000)		Value
Collateralized Mortgage Obligations (continued)
American Home Mortgage Assets Trust
Series 2006-4, Class 1A12, (1 mo. LIBOR US + 0.21%), 0.32%, 10/25/46(d)	USD		2,211	$	1,493,565
Series 2006-5, Class A1, (12 mo. Federal Reserve Cumulative Average US + 0.92%), 1.18%, 11/25/46(d)			3,357		1,485,636
Series 2007-1, Class A1, (12 mo. Federal Reserve Cumulative Average US + 0.70%), 0.96%, 02/25/47(d)			732		421,687
Angel Oak Mortgage Trust, Series 2020-4, Class A3, 2.81%, 06/25/65(a)(d)			3,667		3,722,492
Angel Oak Mortgage Trust I LLC, Series 2019-4, Class A3, 3.30%, 07/26/49(a)(d)			3,443		3,482,797
Angel Oak Mortgage Trust LLC
Series 2020-3, Class A3, 2.87%, 04/25/65(a)(d)			5,512		5,621,646
Series 2020-3, Class M1, 3.81%, 04/25/65(a)(d)			4,120		4,335,379
APS Resecuritization Trust Series 2016-1, Class 1MZ, 4.02%, 07/31/57(a)(d)			7,471		2,652,182
Series 2016-3, Class 3A, (1 mo. LIBOR US + 2.85%), 2.96%, 09/27/46(a)(d)			4,023		4,026,487
Series 2016-3, Class 4A, (1 mo. LIBOR US + 2.60%), 2.71%, 04/27/47(a)(d)			606		604,845
ARI Investments LLC
Series 2017-1, Class A, 4.61%, 01/06/25(b)			2,613		2,593,676
Series 2019-1, 4.55%, 01/30/25(b)			3,062		3,031,708
Banc of America Funding Trust
Series 2014-R2, Class 1C, 0.00%, 11/26/36(a)(d)			3,854		1,034,919
Series 2016-R2, Class 1A1, 4.70%, 05/01/33(a)(d)			1,308		1,257,532
BCAP LLC Trust, Series 2011-RR5, Class 11A5, (1 mo. LIBOR US + 0.15%), 0.42%, 05/28/36(a)(d)			4,498		4,352,564
Bear Stearns ALT-A Trust, Series 2007-1, Class 1A1, (1 mo. LIBOR US + 0.32%), 0.43%, 01/25/47(d)			1,210		1,117,863
Bear Stearns Asset-Backed Securities I Trust, Series 2005-AC9, Class A5, 6.25%, 12/25/35(c)			213		189,062
Bear Stearns Mortgage Funding Trust
Series 2006-SL1, Class A1, (1 mo. LIBOR US + 0.28%), 0.39%, 08/25/36(d)			1,012		997,673
Series 2007-AR2, Class A1, (1 mo. LIBOR US + 0.17%), 0.28%, 03/25/37(d)			302		284,310
Series 2007-AR3, Class 1A1, (1 mo. LIBOR US + 0.14%), 0.25%, 03/25/37(d)			498		470,810
Series 2007-AR4, Class 2A1, (1 mo. LIBOR US + 0.21%), 0.32%, 06/25/37(d)			507		493,004
BlackRock Capital Finance LP, Series 1997-R2, Class AP, 0.00%, 12/25/35(a)(d)(p)			3		2,855
Chase Mortgage Finance Trust, Series 2007— S6, Class 1A1, 6.00%, 12/25/37			22,067		14,078,056
Citicorp Mortgage Securities Trust
Series 2007-9, Class 1A1, 6.25%, 12/25/37			1,580		1,428,650
Series 2008-2, Class 1A1, 6.50%, 06/25/38			4,983		4,395,333
Citigroup Mortgage Loan Trust, Series 2007-2, Class 2A, 6.00%, 11/25/36			10		9,926

64 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Collateralized Mortgage Obligations (continued)
CitiMortgage Alternative Loan Trust, Series 2007-A6, Class 1A11, 6.00%, 06/25/37	USD		772	$	772,896
COLT Mortgage Loan Trust, Series 2020-3, Class A3, 2.38%, 04/27/65(a)(d)			1,883		1,904,639
Countrywide Alternative Loan Trust
Series 2005-22T1, Class A1, (1 mo. LIBOR US + 0.35%), 0.46%, 06/25/35(d)			3,455		2,879,051
Series 2005-72, Class A3, (1 mo. LIBOR US + 0.60%), 0.71%, 01/25/36(d)			561		534,610
Series 2005-76, Class 2A1, (12 mo. Federal Reserve Cumulative Average US + 1.00%), 1.26%, 02/25/36(d)			697		660,016
Series 2006-11CB, Class 3A1, 6.50%, 05/25/36			1,582		1,129,432
Series 2006-15CB, Class A1, 6.50%, 06/25/36			375		277,727
Series 2006-23CB, Class 2A5, (1 mo. LIBOR US + 0.40%), 0.51%, 08/25/36(d)			5,333		933,179
Series 2006-OA14, Class 1A1, (12 mo. Federal Reserve Cumulative Average US + 1.73%), 1.99%, 11/25/46(d)			2,897		2,509,098
Series 2006-OA16, Class A2, (1 mo. LIBOR US + 0.19%), 0.30%, 10/25/46(d)			3,400		3,290,458
Series 2006-OA16, Class A4C, (1 mo. LIBOR US + 0.34%), 0.45%, 10/25/46(d)			4,130		3,231,973
Series 2006-OA21, Class A1, (1 mo. LIBOR US + 0.19%), 0.30%, 03/20/47(d)			7,916		6,681,457
Series 2006-OA8, Class 1A1, (1 mo. LIBOR US + 0.19%), 0.30%, 07/25/46(d)			407		367,948
Series 2006-OC10, Class 2A3, (1 mo. LIBOR US + 0.23%), 0.34%, 11/25/36(d)			1,610		1,506,516
Series 2006-OC7, Class 2A3, (1 mo. LIBOR US + 0.50%), 0.61%, 07/25/46(d)			2,322		2,158,797
Series 2007-3T1, Class 1A1, 6.00%, 04/25/37			325		215,036
Series 2007-OA3, Class 1A1, (1 mo. LIBOR US + 0.14%), 0.25%, 04/25/47(d)			959		862,662
Series 2007-OA8, Class 2A1, (1 mo. LIBOR US + 0.18%), 0.29%, 06/25/47(d)			328		264,012
Series 2007-OH2, Class A2A, (1 mo. LIBOR US + 0.24%), 0.35%, 08/25/47(d)			397		385,113
Countrywide Home Loan Mortgage Pass- Through Trust
Series 2004-29, Class 1A1, (1 mo. LIBOR US + 0.54%), 0.65%, 02/25/35(d)			226		220,885
Series 2006-OA4, Class A1, (12 mo. Federal Reserve Cumulative Average US + 0.96%), 1.22%, 04/25/46(d)			1,384		586,437
Series 2006-OA5, Class 3A1, (1 mo. LIBOR US + 0.40%), 0.51%, 04/25/46(d)			583		546,625
Series 2007-15, Class 2A2, 6.50%, 09/25/37			8,638		5,061,248
Credit Suisse Commercial Mortgage Trust
Series 2014-11R, Class 16A1, 3.20%, 09/27/47(a)(d)			652		673,753
Series 2014-4R, Class 16A3, (1 mo. LIBOR US + 0.20%), 0.32%, 02/27/36(a)(b)(d)			655		614,193
Series 2014-9R, Class 9A1, (1 mo. LIBOR US + 0.12%), 0.24%, 08/27/36(a)(d)			1,181		1,094,139
Series 2019-JR1, Class A1, 4.10%, 09/27/66(a)(d)			22,736		22,836,934

Security		Par (000)		Value
Collateralized Mortgage Obligations (continued)
Credit Suisse Commercial Mortgage Trust Series 2020-SPT1, Class M1, 3.39%, 04/25/65(a)(d)	USD		4,796	$	4,866,096
Credit Suisse Mortgage Capital Certificates, Series 2009-12R, Class 3A1, 6.50%, 10/27/37(a)			8,102		4,385,538
CSFB Mortgage-Backed Pass-Through Certificates, Series 2005-10, Class 10A1, (1 mo. LIBOR US + 1.35%), 1.46%, 11/25/35(d)			1,257		231,374
Deephaven Residential Mortgage Trust
Series 2020-1, Class B2, 4.54%, 01/25/60(a)(d)			1,310		1,334,256
Series 2020-2, Class A3, 2.86%, 05/25/65(a)			3,800		3,893,916
Deutsche Alt-A Securities Mortgage Loan Trust, Series 2007-OA4, Class A2A, (1 mo. LIBOR US + 0.17%), 0.28%, 08/25/47(d)			1,134		1,326,306
Deutsche Alt-A Securities, Inc., Series 2007- RS1, Class A2, (1 mo. LIBOR US + 0.50%), 0.62%, 01/27/37(a)(d)			24		22,664
Deutsche Alt-B Securities Mortgage Loan Trust
Series 2006-AB3, Class A3, 6.51%, 07/25/36(d)			406		394,971
Series 2006-AB3, Class A8, 6.36%, 07/25/36(d)			259		251,870
GreenPoint Mortgage Funding Trust, Series 2006-AR2, Class 4A1, (12 mo. Federal Reserve Cumulative Average US + 2.00%), 2.26%, 03/25/36(d)			788		777,815
GS Mortgage-Backed Securities Corp. Trust, Series 2019-PJ2, Class B4, 4.49%, 11/25/49(a)(d)			1,476		1,502,970
GSR Mortgage Loan Trust
Series 2007-1F, Class 2A4, 5.50%, 01/25/37			150		173,210
Series 2007-OA2, Class 2A1, 2.36%, 06/25/47(d)			1,236		1,016,509
HarborView Mortgage Loan Trust
Series 2006-12, Class 1A1A, (1 mo. LIBOR US + 0.21%), 0.32%, 12/19/36(d)			13,191		12,280,688
Series 2007-4, Class 2A2, (1 mo. LIBOR US + 0.25%), 0.36%, 07/19/47(d)			674		614,654
Homeward Opportunities Fund I Trust
Series 2020-2, Class A2, 2.64%, 05/25/65(a)(d)			4,767		4,878,059
Series 2020-2, Class A3, 3.20%, 05/25/65(a)(d)			5,763		5,894,222
Impac CMB Trust
Series 2004-11, Class 1A2, (1 mo. LIBOR US + 0.52%), 0.63%, 03/25/35(d)			1,116		1,155,944
Series 2005-6, Class 1A1, (1 mo. LIBOR US + 0.50%), 0.62%, 10/25/35(d)			875		863,186
Imperial Fund Mortgage Trust, Series 2020- NQM1, Class A3, 2.05%, 10/25/55(a)(d)			2,471		2,478,295
IndyMac Index Mortgage Loan Trust
Series 2006-AR15, Class A1, (1 mo. LIBOR US + 0.24%), 0.35%, 07/25/36(d)			456		432,711
Series 2007-AR19, Class 3A1, 3.13%, 09/25/37(d)			2,922		2,064,873
Series 2007-FLX5, Class 2A2, (1 mo. LIBOR US + 0.24%), 0.35%, 08/25/37(d)			873		810,700

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 65

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Collateralized Mortgage Obligations (continued)
JPMorgan Alternative Loan Trust
Series 2007-A1, Class 1A4, (1 mo. LIBOR US + 0.42%), 0.53%, 03/25/37(d)	USD		1,443	$	1,424,928
Series 2007-A2, Class 2A1, 3.42%, 05/25/37(d)			301		279,326
JPMorgan Mortgage Trust
Series 2014-OAK4, Class B4, 3.94%, 09/25/44(a)(d)			310		310,187
Series 2021-4, Class B1, 2.90%, 08/25/51(a)(d)			16,120		15,725,866
Series 2021-4, Class B2, 2.90%, 08/25/51(a)(d)			4,090		3,943,015
Series 2021-4, Class B3, 2.90%, 08/25/51(a)(d)			3,860		3,628,019
Legacy Mortgage Asset Trust
Series 2020-GS5, Class A1, 3.25%, 06/25/60(a)			4,115		4,189,552
Series 2020-SL1, Class A, 2.73%, 01/25/60(a)(c)			4,750		4,784,628
Lehman XS Trust
Series 2007-16N, Class AF2, (1 mo. LIBOR US + 0.95%), 1.06%, 09/25/47(d)			3,400		3,527,883
Series 2007-20N, Class A1, (1 mo. LIBOR US + 1.15%), 1.26%, 12/25/37(d)			825		848,094
LHOME Mortgage Trust, Series 2019-RTL1, Class A1, 4.58%, 10/25/23(a)(c)			2,646		2,659,067
MASTR Resecuritization Trust, Series 2008-3, Class A1, 0.55%, 08/25/37(a)(d)			999		523,220
MCM Trust
Series 2018-NPL1, Class B, 0.00%, 05/28/58(a)			4,997		2,671,092
Series 2018-NPL2, Class B, 0.00%, 10/25/28(a)			8,288		4,487,894
Merrill Lynch Alternative Note Asset Trust, Series 2007-OAR2, Class A2, (1 mo. LIBOR US + 0.21%), 0.32%, 04/25/37(d)			1,887		1,837,570
Merrill Lynch Mortgage Investors Trust, Series 2006-A3, Class 6A1, 3.04%, 05/25/36(d)			1,093		1,025,985
MFA Trust, Series 2020-NQM1, Class A3, 2.30%, 08/25/49(a)(d)			545		554,058
Morgan Stanley Resecuritization Trust, Series 2013-R7, Class 1B, (1 mo. LIBOR US + 0.16%), 0.28%, 12/26/46(a)(d)			1,013		992,202
Mortgage Loan Resecuritization Trust, Series 2009-RS1, Class A85, (1 mo. LIBOR US + 0.34%), 0.46%, 04/16/36(a)(d)			3,478		3,206,790
NACC Reperforming Loan REMIC Trust
Series 2004-R1, Class A1, 6.50%, 03/25/34(a)			2,376		2,363,342
Series 2004-R1, Class A2, 7.50%, 03/25/34(a)			545		556,189
New Residential Mortgage Loan Trust
Series 2019-2A, Class A1, 4.25%, 12/25/57(a)(d)			1,558		1,652,389
Series 2020-NPL2, Class A1, 3.23%, 08/25/60(a)(c)			1,562		1,574,203
Series 2020-RPL1, Class B3, 3.91%, 11/25/59(a)(d)			6,210		4,415,229
Series 2020-RPL2, Class A1, 3.58%, 08/25/25(a)(d)			12,699		12,940,398

Security		Par (000)		Value
Collateralized Mortgage Obligations (continued)
Nomura Asset Acceptance Corp. Alternative Loan Trust
Series 2001-R1A, Class A, 7.00%, 02/19/30(a)(d)	USD		413	$	422,282
Series 2006-AF1, Class 1A4, 6.63%, 05/25/36(c)			570		181,120
Series 2007-2, Class A4, (1 mo. LIBOR US + 0.42%), 0.53%, 06/25/37(d)			365		308,630
NYMT Loan Trust, Series 2020-SP2, Class A1, 2.94%, 10/25/60(a)(d)			18,570		18,641,230
Preston Ridge Partners Mortgage LLC
Series 2020-3, Class A1, 2.86%, 09/25/25(a)(c)			23,657		23,826,208
Series 2020-5, Class A1, 3.10%, 11/25/25(a)(c)			17,862		17,985,895
Provident Funding Mortgage Warehouse Securitization Trust, Series 2021-1, Class F, (1 mo. LIBOR US + 4.50%), 0.00%, 02/25/55(a)(b)(d)			2,330		2,330,000
RALI Trust, Series 2007-QH9, Class A1, 1.56%, 11/25/37(d)			665		632,408
Reperforming Loan REMIC Trust
Series 2005-R2, Class 1AF1, (1 mo. LIBOR US + 0.34%), 0.45%, 06/25/35(a)(d)			418		399,490
Series 2005-R3, Class AF, (1 mo. LIBOR US + 0.40%), 0.51%, 09/25/35(a)(d)			129		114,253
Residential Mortgage Loan Trust
Series 2020-2, Class A2, 2.51%, 05/25/60(a)(d)			3,500		3,589,723
Series 2020-2, Class M1, 3.57%, 05/25/60(a)(d)			7,854		8,093,117
RFMSI Series Trust, Series 2006-SA2, Class 2A1, 4.65%, 08/25/36(d)			6,235		5,188,874
Seasoned Credit Risk Transfer Trust, Series 2018-1, Class BX, 1.40%, 05/25/57(d)			539		253,586
Seasoned Loans Structured Transaction Trust, Series 2020-2, Class M1, 4.75%, 09/25/60(a)(d)			15,220		15,653,947
Sequoia Mortgage Trust, Series 2007-3, Class 2AA1, 3.21%, 07/20/37(d)			1,313		1,213,016
Station Place Securitization Trust
Series 2021-WL1, Class E, (1 mo. LIBOR US + 2.00%), 2.11%, 01/26/54(a)(d)			1,720		1,719,457
Series 2021-WL1, Class F, (1 mo. LIBOR US + 2.50%), 2.61%, 01/26/54(a)(d)			1,850		1,849,422
Structured Adjustable Rate Mortgage Loan Trust, Series 2006-3, Class 4A, 3.30%, 04/25/36(d)			781		615,000
Structured Asset Mortgage Investments II Trust
Series 2006-AR4, Class 3A1, (1 mo. LIBOR US + 0.19%), 0.49%, 06/25/36(d)			2,144		2,012,090
Series 2006-AR5, Class 2A1, (1 mo. LIBOR US + 0.42%), 0.53%, 05/25/46(d)			498		444,461
Thornburg Mortgage Securities Trust
Series 2006-3, Class A1, 2.95%, 06/25/46(d)			1,550		1,342,474
Series 2007-3, Class 4A1, (12 mo. LIBOR US + 1.25%), 1.53%, 06/25/47(d)			223		212,625
TVC DSCR
Series 21-1, Class A, 0.00%, 02/01/51(a)			6,844		6,844,457
Series 21-1, Class CERT, 0.00%, 02/01/51(a)			1,711		2,206,653
TVC Mortgage Trust, Series 2020-RTL1, Class A1, 3.47%, 09/25/24(a)			1,960		1,973,548

66 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Collateralized Mortgage Obligations (continued)
Verus Securitization Trust
Series 2019-INV2, Class M1, 3.50%, 07/25/59(a)(d)	USD		660	$	671,283
Series 2020-4, Class A3, 2.32%, 05/25/65(a)(c)			2,772		2,817,145
Series 2020-4, Class M1, 3.29%, 05/25/65(a)(d)			3,120		3,191,254
Series 2020-5, Class M1, 2.60%, 05/25/65(a)(d)			2,312		2,318,635
Series 2020-INV1, Class A2, 3.04%, 03/25/60(a)(d)			1,895		1,960,877
Series 2020-INV1, Class A3, 3.89%, 03/25/60(a)(d)			1,800		1,867,252
Visio Trust
Series 2019-2, Class B1, 3.91%, 11/25/54(a)(d)			906		897,789
Series 2020-1, Class M1, 4.45%, 08/25/55(a)(d)			1,100		1,160,409
Vista Point Securitization Trust
Series 2020-1, Class A1, 1.76%, 03/25/65(a)(d)			11,275		11,401,260
Series 2020-2, Class A3, 2.50%, 04/25/65(a)(d)			3,438		3,477,765
Series 2020-2, Class M1, 3.40%, 04/25/65(a)(d)			1,480		1,501,995
Washington Mutual Mortgage Pass-Through Certificates Trust
Series 2006-1, Class 4CB, 6.50%, 02/25/36			1,239		1,066,294
Series 2006-4, Class 1A1, 6.00%, 04/25/36			3,406		3,407,395
Series 2006-4, Class 3A1, 6.50%, 05/25/36(c)			1,175		1,153,309
Series 2006-4, Class 3A5, 6.35%, 05/25/36(c)			455		447,181
Series 2007-OA5, Class 1A, (12 mo. Federal Reserve Cumulative Average US + 0.75%), 1.01%, 06/25/47(d)			3,285		3,122,446
Series 2007-OA5, Class 2A, (Cost of Funds for the 11th District of San Francisco + 1.25%), 1.71%, 06/25/47(d)			1,687		1,500,638
					438,427,576
Commercial Mortgage-Backed Securities — 3.6%
1211 Avenue of the Americas Trust
Series 2015-1211, Class C, 4.14%, 08/10/35(a)(d)			600		635,991
Series 2015-1211, Class D, 4.14%, 08/10/35(a)(d)			6,157		6,398,713
Series 2015-1211, Class E, 4.14%, 08/10/35(a)(d)			1,110		1,127,109
245 Park Avenue Trust
Series 2017-245P, Class D, 3.66%, 06/05/37(a)(d)			480		481,988
Series 2017-245P, Class E, 3.66%, 06/05/37(a)(d)			2,463		2,356,807
280 Park Avenue Mortgage Trust
Series 2017-280P, Class D, (1 mo. LIBOR US + 1.54%), 1.64%, 09/15/34(a)(d)			2,920		2,916,449
Series 2017-280P, Class E, (1 mo. LIBOR US + 2.12%), 2.23%, 09/15/34(a)(d)			5,835		5,761,745
Series 2017-280P, Class F, (1 mo. LIBOR US + 2.83%), 2.93%, 09/15/34(a)(d)			630		615,137

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
Alen Mortgage Trust, Series 2021-ACEN, Class D, (1 mo. LIBOR US + 3.10%), 3.21%, 04/15/34(a)(d)	USD		2,670	$	2,670,804
AOA Mortgage Trust, Series 2015-1177, Class C, 3.01%, 12/13/29(a)(d)			5,210		5,206,656
Arbor Multifamily Mortgage Securities Trust, Series 2020-MF1, Class E, 1.75%, 05/15/53(a)			636		520,621
Ashford Hospitality Trust, Series 2018-ASHF, Class D, (1 mo. LIBOR US + 2.10%), 2.21%, 04/15/35(a)(d)			740		726,160
Atrium Hotel Portfolio Trust
Series 2017-ATRM, Class D, (1 mo. LIBOR US + 1.95%), 2.06%, 12/15/36(a)(d)			4,840		4,621,428
Series 2017-ATRM, Class E, (1 mo. LIBOR US + 3.05%), 3.16%, 12/15/36(a)(d)			568		537,509
Banc of America Merrill Lynch Commercial Mortgage Securities Trust
Series 2015-200P, Class F, 3.60%, 04/14/33(a)(d)			2,691		2,759,531
Series 2016-ISQ, Class C, 3.61%, 08/14/34(a)(d)			445		466,563
Series 2017-SCH, Class AF, (1 mo. LIBOR US + 1.00%), 1.11%, 11/15/33(a)(d)			150		146,425
Series 2017-SCH, Class BF, (1 mo. LIBOR US + 1.40%), 1.51%, 11/15/33(a)(d)			2,870		2,789,181
Series 2017-SCH, Class CL, (1 mo. LIBOR US + 1.50%), 1.61%, 11/15/32(a)(d)			970		837,624
Series 2017-SCH, Class DL, (1 mo. LIBOR US + 2.00%), 2.11%, 11/15/32(a)(d)			1,930		1,595,164
Series 2018-DSNY, Class C, (1 mo. LIBOR US + 1.35%), 1.46%, 09/15/34(a)(d)			350		347,395
Series 2018-DSNY, Class D, (1 mo. LIBOR US + 1.70%), 1.81%, 09/15/34(a)(d)			3,275		3,234,347
BANK
Series 2019-BN21, Class A5, 2.85%, 10/17/52			1,088		1,130,275
Series 2020-BN28, Class D, 2.50%, 03/15/63(a)			610		537,038
Series 2021-BN32, Class A5, 2.64%, 04/15/54			1,970		2,006,381
Bayview Commercial Asset Trust
Series 2005-3A, Class A1, (1 mo. LIBOR US + 0.48%), 0.59%, 11/25/35(a)(d)			2,217		2,090,863
Series 2005-4A, Class A1, (1 mo. LIBOR US + 0.45%), 0.56%, 01/25/36(a)(d)			4,690		4,448,342
Series 2005-4A, Class A2, (1 mo. LIBOR US + 0.59%), 0.69%, 01/25/36(a)(d)			73		69,530
Series 2005-4A, Class M1, (1 mo. LIBOR US + 0.68%), 0.78%, 01/25/36(a)(d)			194		186,034
Series 2006-1A, Class A2, (1 mo. LIBOR US + 0.54%), 0.65%, 04/25/36(a)(d)			255		241,199
Series 2006-2A, Class A2, (1 mo. LIBOR US + 0.42%), 0.53%, 07/25/36(a)(d)			860		824,923
Series 2006-3A, Class A1, (1 mo. LIBOR US + 0.25%), 0.36%, 10/25/36(a)(d)			420		399,590
Series 2006-3A, Class A2, (1 mo. LIBOR US + 0.30%), 0.41%, 10/25/36(a)(d)			292		279,177
Series 2006-4A, Class A1, (1 mo. LIBOR US + 0.23%), 0.34%, 12/25/36(a)(d)			1,570		1,500,560
Series 2007-2A, Class A1, (1 mo. LIBOR US + 0.27%), 0.38%, 07/25/37(a)(d)			9,435		8,934,406

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 67

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
Bayview Commercial Asset Trust
Series 2007-6A, Class A4A, (1 mo. LIBOR US + 1.50%), 1.61%, 12/25/37(a)(d)	USD		1,980	$	1,932,125
Series 2008-2, Class A4A, (1 mo. LIBOR US + 2.50%), 2.61%, 04/25/38(a)(d)			2,890		2,922,031
BBCMS Mortgage Trust
Series 2018-CHRS, Class E, 4.27%, 08/05/38(a)(d)			980		835,420
Series 2018-TALL, Class A, (1 mo. LIBOR US + 0.72%), 0.83%, 03/15/37(a)(d)			918		908,811
Series 2018-TALL, Class D, (1 mo. LIBOR US + 1.45%), 1.55%, 03/15/37(a)(d)			1,120		1,092,350
Series 2019-BWAY, Class D, (1 mo. LIBOR US + 2.16%), 2.27%, 11/15/34(a)(d)			1,118		1,101,671
BBCMS Trust, Series 2015-SRCH, Class A1, 3.31%, 08/10/35(a)			2,535		2,695,371
BB-UBS Trust, Series 2012-SHOW, Class E, 4.03%, 11/05/36(a)(d)			790		648,007
Bear Stearns Commercial Mortgage Securities Trust
Series 2005-PWR7, Class B, 4.97%, 02/11/41(d)			390		387,039
Series 2007-T26, Class AM, 5.43%, 01/12/45(d)			747		743,859
Benchmark Mortgage Trust
Series 2018-B3, Class D, 3.06%, 04/10/51(a)(d)			210		188,837
Series 2018-B5, Class A3, 3.94%, 07/15/51			4,840		5,406,190
Series 2019-B10, Class 3CCA, 3.90%, 03/15/62(a)(d)			3,610		3,763,881
Series 2019-B14, Class 225C, 3.29%, 12/15/62(a)(d)			1,411		1,375,615
Series 2020-B16, Class D, 2.50%, 02/15/53(a)			38		32,040
BFLD Trust, Series 2020-EYP, Class E, (1 mo. LIBOR US + 3.70%), 3.81%, 10/15/35(a)(d)			5,885		5,958,572
BHMS, Series 2018-ATLS, Class A, (1 mo. LIBOR US + 1.25%), 1.36%, 07/15/35(a)(d)			2,770		2,768,283
BWAY Mortgage Trust
Series 2013-1515, Class A2, 3.45%, 03/10/33(a)			3,004		3,217,174
Series 2013-1515, Class D, 3.63%, 03/10/33(a)			1,400		1,461,946
Series 2013-1515, Class E, 3.72%, 03/10/33(a)			250		258,063
Series 2013-1515, Class F, 3.93%, 03/10/33(a)(d)			250		256,043
Series 2015-1740, Class E, 4.45%, 01/10/35(a)(d)			478		450,378
BX Commercial Mortgage Trust
Series 2018-BIOA, Class E, (1 mo. LIBOR US + 1.95%), 2.06%, 03/15/37(a)(d)			1,210		1,209,986
Series 2018-BIOA, Class F, (1 mo. LIBOR US + 2.47%), 2.58%, 03/15/37(a)(d)			8,300		8,290,276
Series 2018-IND, Class G, (1 mo. LIBOR US + 2.05%), 2.16%, 11/15/35(a)(d)			2,324		2,322,546
Series 2018-IND, Class H, (1 mo. LIBOR US + 3.00%), 3.11%, 11/15/35(a)(d)			11,634		11,637,553
Series 2019-XL, Class G, (1 mo. LIBOR US + 2.30%), 2.41%, 10/15/36(a)(d)			20,429		20,414,861
Series 2019-XL, Class J, (1 mo. LIBOR US + 2.65%), 2.76%, 10/15/36(a)(d)			28,293		28,275,682

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
BX Commercial Mortgage Trust
Series 2020-BXLP, Class F, (1 mo. LIBOR US + 2.00%), 2.11%, 12/15/36(a)(d)	USD		22,530	$	22,503,236
Series 2020-BXLP, Class G, (1 mo. LIBOR US + 2.50%), 2.61%, 12/15/36(a)(d)			6,776		6,768,116
Series 2020-FOX, Class E, (1 mo. LIBOR US + 3.60%), 3.71%, 11/15/32(a)(d)			7,490		7,511,099
Series 2020-VIV3, Class B, 3.54%, 03/09/44(a)(d)			2,940		3,084,387
Series 2020-VIV4, Class A, 2.84%, 03/09/44(a)			5,380		5,458,245
Series 2020-VKNG, Class F, (1 mo. LIBOR US + 2.75%), 2.86%, 10/15/37(a)(d)			4,670		4,669,993
Series 2021-NWM, Class A, (1 mo. LIBOR US + 0.91%), 1.06%, 02/15/33(a)(b)(d)			17,038		17,038,000
Series 2021-NWM, Class B, (1 mo. LIBOR US + 2.15%), 2.30%, 02/15/33(a)(b)(d)			10,439		10,439,000
Series 2021-NWM, Class C, (1 mo. LIBOR US + 4.25%), 4.40%, 02/15/33(a)(b)(d)			6,988		6,988,000
BX Trust
Series 2019-OC11, Class A, 3.20%, 12/09/41(a)			1,183		1,236,118
Series 2019-OC11, Class D, 4.08%, 12/09/41(a)(d)			8,267		8,586,658
Series 2019-OC11, Class E, 4.08%, 12/09/41(a)(d)			11,936		11,870,548
Series 2021-LBA, Class FJV, (1 mo. LIBOR US + 2.40%), 2.51%, 02/15/36(a)(d)			6,390		6,390,028
Series 2021-LBA, Class FV, (1 mo. LIBOR US + 2.40%), 2.51%, 02/15/36(a)(d)			5,128		5,121,745
Series 2021-LBA, Class GJV, (1 mo. LIBOR US + 3.00%), 3.11%, 02/15/36(a)(d)			8,390		8,400,259
Series 2021-LBA, Class GV, (1 mo. LIBOR US + 3.00%), 3.11%, 02/15/36(a)(d)			6,640		6,648,119
Series 2021-MFM1, Class E, (1 mo. LIBOR US + 2.25%), 2.36%, 01/15/34(a)(d)			1,650		1,648,018
Series 2021-MFM1, Class F, (1 mo. LIBOR US + 3.00%), 3.11%, 01/15/34(a)(d)			2,550		2,548,464
BXP Trust
Series 2017-CC, Class D, 3.55%, 08/13/37(a)(d)			750		784,570
Series 2017-CC, Class E, 3.55%, 08/13/37(a)(d)			1,450		1,458,215
Series 2017-GM, Class D, 3.43%, 06/13/39(a)(d)			590		604,126
Series 2017-GM, Class E, 3.43%, 06/13/39(a)(d)			1,240		1,236,549
CAMB Commercial Mortgage Trust, Series 2019-LIFE, Class D, (1 mo. LIBOR US + 1.75%), 1.86%, 12/15/37(a)(d)			3,619		3,619,582
CD Mortgage Trust
Series 2017-CD5, Class B, 3.96%, 08/15/50(d)			2,091		2,240,918
Series 2017-CD6, Class C, 4.27%, 11/13/50(d)			1,290		1,353,511
CFCRE Commercial Mortgage Trust
Series 2016-C3, Class A3, 3.87%, 01/10/48			410		450,650
Series 2018-TAN, Class A, 4.24%, 02/15/33(a)			1,860		1,941,504
Series 2018-TAN, Class B, 4.69%, 02/15/33(a)			2,274		2,364,658

68 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
CFCRE Commercial Mortgage Trust
Series 2018-TAN, Class C, 5.30%, 02/15/33(a)	USD		1,160	$	1,211,265
Series 2018-TAN, Class E, 6.45%, 02/15/33(a)(d)			670		694,352
CFK Trust, Series 2019-FAX, Class D, 4.64%, 01/15/39(a)(d)			2,643		2,861,115
CHC Commercial Mortgage Trust, Series 2019- CHC, Class B, (1 mo. LIBOR US + 1.50%), 1.61%, 06/15/34(a)(d)			7,262		7,170,651
Citigroup Commercial Mortgage Trust
Series 2014-GC19, Class C, 5.09%, 03/10/47(d)			440		470,350
Series 2015-GC27, Class B, 3.77%, 02/10/48			990		1,053,416
Series 2016-C1, Class D, 4.95%, 05/10/49(a)(d)			450		412,387
Series 2016-GC37, Class C, 4.93%, 04/10/49(d)			640		668,826
Series 2016-P3, Class C, 4.89%, 04/15/49(d)			30		31,277
Series 2016-P3, Class D, 2.80%, 04/15/49(a)(d)			137		94,569
Series 2017-C4, Class A4, 3.47%, 10/12/50			1,220		1,329,971
Series 2018-C6, Class A4, 4.41%, 11/10/51			1,960		2,243,338
Series 2019-C7, Class A4, 3.10%, 12/15/72			1,130		1,195,685
Series 2019-PRM, Class D, 4.35%, 05/10/36(a)			1,120		1,163,425
Series 2019-PRM, Class E, 4.73%, 05/10/36(a)(d)			5,271		5,422,732
Series 2019-PRM, Class F, 4.73%, 05/10/36(a)(d)			5,180		5,213,717
Series 2019-SMRT, Class D, 4.75%, 01/10/36(a)(d)			7,200		7,701,319
Series 2019-SMRT, Class E, 4.75%, 01/10/36(a)(d)			419		432,625
Series 2019-SST2, Class F, (1 mo. LIBOR US + 2.50%), 2.61%, 12/15/36(a)(d)			1,090		1,088,694
Series 2020-420K, Class E, 3.31%, 11/10/42(a)(d)			1,540		1,427,292
Citigroup/Deutsche Bank Commercial Mortgage Trust
Series 2006-CD3, Class AM, 5.65%, 10/15/48			1,864		1,912,628
Series 2017-CD3, Class A4, 3.63%, 02/10/50			850		932,881
Cold Storage Trust
Series 2020-ICE5, Class E, (1 mo. LIBOR US + 2.77%), 2.87%, 11/15/37(a)(d)			9,270		9,284,467
Series 2020-ICE5, Class F, (1 mo. LIBOR US + 3.49%), 3.60%, 11/15/37(a)(d)			4,266		4,292,899
Commercial Mortgage Pass-Through Certificates
Series 2014-CR15, Class C, 4.74%, 02/10/47(d)			3,920		4,229,743
Series 2014-CR18, Class A4, 3.55%, 07/15/47			371		396,879
Series 2015-LC21, Class C, 4.34%, 07/10/48(d)			1,600		1,634,828
Series 2017-COR2, Class D, 3.00%, 09/10/50(a)			179		160,707
Series 2018-HCLV, Class B, (1 mo. LIBOR US + 1.40%), 1.51%, 09/15/33(a)(d)			1,420		1,404,075

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
Commercial Mortgage Trust
Series 2013-GAM, Class A2, 3.37%, 02/10/28(a)	USD		1,552	$	1,539,807
Series 2013-GAM, Class E, 3.43%, 02/10/28(a)(d)			2,270		2,067,669
Series 2014-CR21, Class A3, 3.53%, 12/10/47			1,334		1,423,069
Series 2015-LC19, Class D, 2.87%, 02/10/48(a)			76		73,203
Series 2015-LC23, Class A4, 3.77%, 10/10/48			1,040		1,143,425
Series 2016-667M, Class D, 3.18%, 10/10/36(a)(d)			630		605,970
CORE Mortgage Trust, Series 2019-CORE, Class F, (1 mo. LIBOR US + 2.35%), 2.46%, 12/15/31(a)(d)			3,087		3,050,836
Credit Suisse Commercial Mortgage Trust
Series 2017-CALI, Class C, 3.78%, 11/10/32(a)(d)			1,729		1,819,250
Series 2017-PFHP, Class A, (1 mo. LIBOR US + 0.95%), 1.06%, 12/15/30(a)(d)			900		893,849
Series 2017-TIME, Class A, 3.65%, 11/13/39(a)			850		858,516
Series 2020-FACT, Class E, (1 mo. LIBOR US + 4.86%), 4.97%, 10/15/37(a)(d)			4,380		4,450,265
Series 2020-NET, Class D, 3.70%, 08/15/37(a)(d)			710		723,555
Series 2020-NET, Class E, 3.70%, 08/15/37(a)(d)			3,580		3,546,245
Credit Suisse Mortgage Capital Certificates, Series 2019-ICE4, Class E, (1 mo. LIBOR US + 2.15%), 2.26%, 05/15/36(a)(d)			2,600		2,603,955
CSAIL Commercial Mortgage Trust
Series 2015-C2, Class A4, 3.50%, 06/15/57			1,160		1,252,357
Series 2016-C5, Class B, 4.46%, 11/15/48(d)			2,410		2,623,348
Series 2018-C14, Class C, 4.89%, 11/15/51(d)			300		329,756
Series 2018-CX12, Class A4, 4.22%, 08/15/51(d)			460		517,579
Series 2018-CX12, Class C, 4.76%, 08/15/51(d)			570		583,115
Series 2019-C15, Class A4, 4.05%, 03/15/52			4,080		4,552,223
Series 2019-C15, Class D, 3.00%, 03/15/52(a)			294		248,252
Series 2019-C16, Class C, 4.24%, 06/15/52(d)			2,919		2,943,979
Series 2019-C17, Class C, 3.93%, 09/15/52			3,158		3,133,157
Series 2019-C17, Class D, 2.50%, 09/15/52(a)			1,601		1,345,387
Series 2020-C19, Class A3, 2.56%, 03/15/53			6,155		6,201,724
DBGS Mortgage Trust
Series 2018-5BP, Class B, (1 mo. LIBOR US + 0.83%), 0.94%, 06/15/33(a)(d)			2,890		2,886,460
Series 2019-1735, Class F, 4.20%, 04/10/37(a)(d)			1,144		926,087
Del Amo Fashion Center Trust, Series 2017- AMO, Class D, 3.64%, 06/05/35(a)(d)			962		716,146
Deutsche Bank JPMorgan Mortgage Trust, Series 2016-C1, Class A4, 3.28%, 05/10/49			1,430		1,537,553
Deutsche Bank UBS Mortgage Trust Series 2017-BRBK, Class A, 3.45%, 10/10/34(a)			2,540		2,707,691

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 69

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
Deutsche Bank UBS Mortgage Trust
Series 2017-BRBK, Class D, 3.53%, 10/10/34(a)(d)	USD		1,800	$	1,870,537
Series 2017-BRBK, Class E, 3.53%, 10/10/34(a)(d)			3,560		3,633,314
Series 2017-BRBK, Class F, 3.53%, 10/10/34(a)(d)			1,270		1,279,296
Exantas Capital Corp. Ltd., Series 2019-RSO7, Class AS, (1 mo. LIBOR US + 1.50%), 1.61%, 04/15/36(a)(d)			3,495		3,505,620
FREMF Mortgage Trust
Series 2017-KGX1, Class BFX, 3.59%, 10/25/27(a)(d)			1,190		1,219,453
Series 2018-K74, Class B, 4.09%, 02/25/51(a)(d)			120		130,899
Series 2018-K80, Class B, 4.23%, 08/25/50(a)(d)			1,510		1,672,924
Series 2018-KHG1, Class C, 3.81%, 12/25/27(a)(d)			4,579		3,996,524
FRESB Mortgage Trust, Series 2018-SB53, Class A10F, 3.65%, 06/25/28(d)			1,304		1,407,050
GCT Commercial Mortgage Trust
Series 2021-GCT, Class A, (1 mo. LIBOR US + 0.80%), 0.91%, 02/15/38(a)(d)			1,870		1,870,352
Series 2021-GCT, Class D, (1 mo. LIBOR US + 2.35%), 2.46%, 02/15/38(a)(d)			440		440,496
GPMT Ltd., Series 2018-FL1, Class A, (1 mo. LIBOR US + 0.90%), 1.01%, 11/21/35(a)(d)			377		375,653
Grace Trust, Series 2020-GRCE, Class E, 2.68%, 12/10/40(a)(d)			3,335		3,054,636
GS Mortgage Securities Corp. II
Series 2005-ROCK, Class A, 5.37%, 05/03/32(a)			2,750		3,166,281
Series 2012-TMSQ, Class D, 3.46%, 12/10/30(a)(d)			1,210		1,100,028
GS Mortgage Securities Corp. Trust
Series 2017-GPTX, Class A, 2.86%, 05/10/34(a)			2,290		2,279,456
Series 2019-BOCA, Class A, (1 mo. LIBOR US + 1.20%), 1.31%, 06/15/38(a)(d)			1,431		1,432,498
Series 2019-SOHO, Class A, (1 mo. LIBOR US + 0.90%), 1.01%, 06/15/36(a)(d)			3,715		3,710,267
Series 2019-SOHO, Class E, (1 mo. LIBOR US + 1.87%), 1.98%, 06/15/36(a)(d)			1,723		1,636,235
Series 2020-TWN3, Class B, (1 mo. LIBOR US + 2.50%), 2.61%, 11/15/37(a)(d)			320		321,539
Series 2020-TWN3, Class D, (1 mo. LIBOR US + 3.70%), 3.81%, 11/15/37(a)(d)			200		202,305
GS Mortgage Securities Trust
Series 2012-GCJ9, Class C, 4.45%, 11/10/45(a)(d)			1,507		1,564,534
Series 2014-GC20, Class B, 4.53%, 04/10/47(d)			140		142,399
Series 2015-590M, Class E, 3.81%, 10/10/35(a)(d)			1,790		1,773,511
Series 2015-GC32, Class C, 4.42%, 07/10/48(d)			290		308,775
Series 2015-GS1, Class A3, 3.73%, 11/10/48			670		736,094
Series 2017-GS7, Class D, 3.00%, 08/10/50(a)			530		474,179
Series 2017-GS7, Class E, 3.00%, 08/10/50(a)			180		155,613

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
GS Mortgage Securities Trust Series 2019-GSA1, Class C, 3.81%, 11/10/52(d)	USD		520	$	533,021
GSCG Trust, Series 2019-600C, Class F, 3.99%, 09/06/34(a)(d)			3,090		2,957,909
HMH Trust, Series 2017-NSS, Class A, 3.06%, 07/05/31(a)			3,390		3,378,605
Hudson Yards Mortgage Trust
Series 2019-30HY, Class E, 3.44%, 07/10/39(a)(d)			2,178		2,170,801
Series 2019-55HY, Class F, 2.94%, 12/10/41(a)(d)			4,179		3,886,625
IMT Trust
Series 2017-APTS, Class AFX, 3.48%, 06/15/34(a)			1,540		1,631,973
Series 2017-APTS, Class DFX, 3.50%, 06/15/34(a)(d)			1,600		1,650,058
Series 2017-APTS, Class EFX, 3.50%, 06/15/34(a)(d)			810		820,430
Independence Plaza Trust
Series 2018-INDP, Class B, 3.91%, 07/10/35(a)			700		734,504
Series 2018-INDP, Class C, 4.16%, 07/10/35(a)			1,600		1,668,579
JPMBB Commercial Mortgage Securities Trust
Series 2014-C22, Class B, 4.55%, 09/15/47(d)			670		698,621
Series 2015-C33, Class D1, 4.11%, 12/15/48(a)(d)			1,873		1,815,700
JPMDB Commercial Mortgage Securities Trust, Series 2018-C8, Class A4, 4.21%, 06/15/51			965		1,089,187
JPMorgan Chase Commercial Mortgage Securities Trust
Series 2012-CBX, Class A4FL, (1 mo. LIBOR US + 1.30%), 1.41%, 06/15/45(a)(d)			338		338,885
Series 2015-JP1, Class C, 4.73%, 01/15/49(d)			710		776,618
Series 2016-NINE, Class A, 2.85%, 09/06/38(a)(d)			647		684,660
Series 2017-FL10, Class E, (1 mo. LIBOR US + 3.90%), 4.01%, 06/15/32(a)(d)			560		556,646
Series 2017-JP5, Class D, 4.62%, 03/15/50(a)(d)			1,430		1,397,068
Series 2017-JP6, Class A5, 3.49%, 07/15/50			1,180		1,283,532
Series 2017-JP7, Class B, 4.05%, 09/15/50			320		344,479
Series 2018-AON, Class A, 4.13%, 07/05/31(a)			2,825		3,015,538
Series 2018-AON, Class D, 4.61%, 07/05/31(a)(d)			1,518		1,593,892
Series 2018-WPT, Class DFX, 5.35%, 07/05/33(a)			1,996		2,102,437
Series 2019-BKWD, Class E, (1 mo. LIBOR US + 2.60%), 2.71%, 09/15/29(a)(d)			2,450		2,425,351
Series 2019-COR5, Class A3, 3.12%, 06/13/52			1,700		1,798,694
Series 2019-COR5, Class C, 3.75%, 06/13/52			988		994,555
Series 2019-MFP, Class E, (1 mo. LIBOR US + 2.16%), 2.27%, 07/15/36(a)(d)			2,460		2,429,911
Series 2019-MFP, Class F, (1 mo. LIBOR US + 3.00%), 3.11%, 07/15/36(a)(d)			4,361		4,281,277

70 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
JPMorgan Chase Commercial Mortgage Securities Trust
Series 2019-OSB, Class E, 3.78%, 06/05/39(a)(d)	USD		1,384	$	1,364,149
Series 2020-609M, Class D, (1 mo. LIBOR US + 2.77%), 2.88%, 10/15/33(a)(d)			1,600		1,605,486
Series 2020-MKST, Class E, (1 mo. LIBOR US + 2.25%), 2.36%, 12/15/36(a)(d)			1,973		1,898,069
KKR Industrial Portfolio Trust, Series 2021- KDIP, Class F, (1 mo. LIBOR US + 2.05%), 2.16%, 12/15/37(a)(d)			3,320		3,321,485
KNDL Mortgage Trust
Series 2019-KNSQ, Class E, (1 mo. LIBOR US + 1.80%), 1.91%, 05/15/36(a)(d)			11,283		11,268,758
Series 2019-KNSQ, Class F, (1 mo. LIBOR US + 2.00%), 2.11%, 05/15/36(a)(d)			2,550		2,451,521
Ladder Capital Commercial Mortgage Trust
Series 2014-909, Class A, 3.39%, 05/15/31(a)			2,030		2,028,422
Series 2014-909, Class C, 3.90%, 05/15/31(a)(d)			2,560		2,557,138
Series 2014-909, Class D, 3.90%, 05/15/31(a)(d)			4,633		4,625,945
Lehman Brothers Small Balance Commercial Mortgage Trust
Series 2006-2A, Class M2, (1 mo. LIBOR US + 0.39%), 0.50%, 09/25/36(a)(d)			243		238,795
Series 2007-1A, Class 1A, (1 mo. LIBOR US + 0.25%), 0.36%, 03/25/37(a)(d)			598		578,979
Life Mortgage Trust, Series 2021-BMR, Class F, (1 mo. LIBOR US + 2.35%), 2.46%, 03/15/38(a)(d)			7,980		7,992,765
LSTAR Commercial Mortgage Trust, Series 2015-3, Class AS, 3.17%, 04/20/48(a)(d)			1,033		1,043,175
MAD Mortgage Trust
Series 2017-330M, Class D, 3.71%, 08/15/34(a)(d)			1,085		1,106,846
Series 2017-330M, Class E, 3.76%, 08/15/34(a)(d)			1,846		1,853,372
Manhattan West, Series 2020-1MW, Class D, 2.34%, 09/10/39(a)(d)			1,259		1,227,480
MFT Trust
Series 2020-ABC, Class C, 3.48%, 02/10/42(a)(d)			6,719		6,460,487
Series 2020-ABC, Class D, 3.48%, 02/10/42(a)(d)			4,800		4,430,688
Morgan Stanley Bank of America Merrill Lynch Trust
Series 2015-C23, Class A4, 3.72%, 07/15/50			1,016		1,104,985
Series 2015-C23, Class D, 4.15%, 07/15/50(a)(d)			110		108,119
Series 2015-C25, Class B, 4.53%, 10/15/48(d)			2,910		3,217,456
Series 2015-C25, Class C, 4.53%, 10/15/48(d)			430		458,912
Series 2015-C26, Class D, 3.06%, 10/15/48(a)			209		200,475
Series 2017-C33, Class C, 4.56%, 05/15/50(d)			840		856,560

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
Morgan Stanley Capital Barclays Bank Trust, Series 2016-MART, Class A, 2.20%, 09/13/31(a)	USD		820	$	820,492
Morgan Stanley Capital I Trust
Series 2006-IQ11, Class C, 5.99%, 10/15/42(d)			248		247,148
Series 2007-T27, Class AJ, 6.02%, 06/11/42(d)			1,722		1,783,511
Series 2014-150E, Class D, 4.30%, 09/09/32(a)(d)			3,015		3,082,458
Series 2014-150E, Class F, 4.30%, 09/09/32(a)(d)			508		484,058
Series 2014-CPT, Class E, 3.45%, 07/13/29(a)(d)			250		249,968
Series 2015-MS1, Class A4, 3.78%, 05/15/48(d)			420		460,821
Series 2015-MS1, Class C, 4.03%, 05/15/48(d)			1,000		956,553
Series 2015-MS1, Class D, 4.03%, 05/15/48(a)(d)			310		272,582
Series 2017-CLS, Class E, (1 mo. LIBOR US + 1.95%), 2.06%, 11/15/34(a)(d)			471		471,148
Series 2017-CLS, Class F, (1 mo. LIBOR US + 2.60%), 2.71%, 11/15/34(a)(d)			6,092		6,084,688
Series 2017-H1, Class C, 4.28%, 06/15/50(d)			560		570,547
Series 2017-H1, Class D, 2.55%, 06/15/50(a)			4,190		3,402,804
Series 2017-HR2, Class D, 2.73%, 12/15/50(b)			430		365,500
Series 2018-H3, Class A5, 4.18%, 07/15/51			175		195,840
Series 2018-H3, Class C, 4.85%, 07/15/51(d)			420		455,983
Series 2018-H4, Class C, 5.08%, 12/15/51(d)			670		707,506
Series 2018-L1, Class A3, 4.14%, 10/15/51			940		1,043,025
Series 2018-MP, Class E, 4.28%, 07/11/40(a)(d)			3,305		2,889,750
Series 2018-SUN, Class A, (1 mo. LIBOR US + 0.90%), 1.01%, 07/15/35(a)(d)			1,410		1,409,138
Series 2018-SUN, Class F, (1 mo. LIBOR US + 2.55%), 2.66%, 07/15/35(a)(d)			417		411,800
Series 2019-L2, Class A4, 4.07%, 03/15/52			1,485		1,662,273
Series 2019-NUGS, Class E, (1 mo. LIBOR US + 2.24%), 3.74%, 12/15/36(a)(d)			1,066		1,068,615
Series 2020-L4, Class D, 2.50%, 02/15/53(a)			120		104,367
Morgan Stanley Capital I, Inc., Series 2018-H3, Class D, 3.00%, 07/15/51(a)			549		486,505
MSCG Trust, Series 2018-SELF, Class F, (1 mo. LIBOR US + 3.05%), 3.16%, 10/15/37(a)(d)			3,450		3,477,012
MSDB Trust, Series 2017-712F, Class B, 3.45%, 07/11/39(a)(d)			1,650		1,680,353
Natixis Commercial Mortgage Securities Trust
Series 2018-FL1, Class A, (1 mo. LIBOR US + 0.95%), 1.06%, 06/15/35(a)(d)			753		743,952
Series 2018-FL1, Class MCR1, (1 mo. LIBOR US + 2.35%), 2.46%, 06/15/35(a)(d)			646		635,998
Series 2018-SOX, Class A, 4.40%, 06/17/38(a)			4,162		4,455,681
Series 2019-LVL, Class D, 4.44%, 08/15/38(a)			1,550		1,496,907
Series 2020-AGC, Class A, (1 mo. LIBOR US + 2.55%), 2.95%, 08/18/25(a)(d)			23,760		23,829,757
Olympic Tower Mortgage Trust, Series 2017-OT, Class E, 3.95%, 05/10/39(a)(d)			2,910		2,564,441

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 71

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
One Market Plaza Trust, Series 2017-1MKT, Class D, 4.15%, 02/10/32(a)	USD		4,327	$	4,419,761
One New York Plaza Trust, Series 2020-1NYP, Class D, (1 mo. LIBOR US + 2.75%), 2.86%, 01/15/26(a)(d)			960		969,598
PFP Ltd.
Series 2019-5, Class A, (1 mo. LIBOR US + 0.97%), 1.08%, 04/14/36(a)(d)			754		754,085
Series 2019-5, Class AS, (1 mo. LIBOR US + 1.42%), 1.53%, 04/14/36(a)(d)			900		899,036
Prima Capital CRE Securitization Ltd.
Series 2015-4A, Class C, 4.00%, 08/24/49(a)(b)			1,590		1,572,828
Series 2016-6A, Class C, 4.00%, 08/24/40(a)(b)			7,170		7,121,961
Scorpio European Loan Conduit No. 34 DAC, Series 34A, Class C, (3 mo. LIBOR GBP + 2.10%), 2.16%, 05/17/29(a)(d)	GBP		1,184		1,604,770
SG Commercial Mortgage Securities Trust, Series 2019-PREZ, Class D, 3.48%, 09/15/39(a)(d)	USD		2,200		2,127,267
U.S.
Series 2018-USDC, Class E, 4.49%, 05/13/38(a)(d)			1,890		1,611,902
Series 2018-USDC, Class F, 4.49%, 05/13/38(a)(d)			1,420		1,032,620
UBS Commercial Mortgage Trust, Series 2017-C7, Class A4, 3.68%, 12/15/50			880		963,432
UBS-Barclays Commercial Mortgage Trust, Series 2012-C3, Class D, 5.03%, 08/10/49(a)(d)			570		582,948
VCC Trust, Series 2020-MC1, Class A, 4.50%, 06/25/45(a)(d)			12,961		12,995,416
Velocity Commercial Capital Loan Trust Series 2014-1, Class M7, 7.94%, 09/25/44(a)(d)			2,399		2,174,391
Series 2016-1, Class M4, 8.65%, 04/25/46(a)(d)			370		382,895
Series 2016-2, Class M2, 4.46%, 10/25/46(d) .			91		91,364
Series 2016-2, Class M3, 5.50%, 10/25/46(d) .			800		806,277
Series 2016-2, Class M4, 7.23%, 10/25/46(d) .			370		376,729
Series 2017-1, Class M2, 4.45%, 05/25/47(a)(d)			410		416,368
Series 2017-1, Class M3, 5.35%, 05/25/47(a)(d)			410		422,805
Series 2017-2, Class M3, 4.24%, 11/25/47(a)(d)			474		469,375
Series 2017-2, Class M4, 5.00%, 11/25/47(a)(d)			286		280,802
Series 2018-1, Class M2, 4.26%, 04/25/48(a) .			315		324,662
Series 2020-1, Class M1, 2.80%, 02/25/50(a)(d)			1,224		1,238,589
Series 2020-1, Class M2, 2.98%, 02/25/50(a)(d)			1,163		1,174,172
VNDO Trust, Series 2016-350P, Class D, 3.90%, 01/10/35(a)(d)			3,390		3,424,292
Wells Fargo Commercial Mortgage Trust
Series 2015-P2, Class D, 3.24%, 12/15/48(a)			884		730,118
Series 2016-C32, Class A3FL, (1 mo. LIBOR US + 1.42%), 1.53%, 01/15/59(d)			3,225		3,223,879
Series 2016-C34, Class A3FL, (1 mo. LIBOR US + 1.04%), 1.15%, 06/15/49(a)(d)			1,830		1,850,624

Security		Par (000)		Value
Commercial Mortgage-Backed Securities (continued)
Wells Fargo Commercial Mortgage Trust
Series 2016-NXS5, Class B, 4.96%, 01/15/59(d)	USD		860	$	956,000
Series 2017-C39, Class D, 4.35%, 09/15/50(a)(d)			594		510,963
Series 2017-C41, Class B, 4.19%, 11/15/50(d)			1,710		1,825,612
Series 2017-C41, Class D, 2.60%, 11/15/50(a)(d)			1,172		927,277
Series 2017-HSDB, Class A, (1 mo. LIBOR US + 0.85%), 0.96%, 12/13/31(a)(d)			1,508		1,483,075
Series 2018-1745, Class A, 3.75%, 06/15/36(a)(d)			1,987		2,168,127
Series 2018-C44, Class D, 3.00%, 05/15/51(a)			348		303,922
Series 2018-C45, Class C, 4.73%, 06/15/51			530		556,740
Series 2018-C48, Class B, 4.90%, 01/15/52(d)			3,612		4,127,051
Series 2019-C52, Class C, 3.56%, 08/15/52			465		454,636
Series 2020-SDAL, Class D, (1 mo. LIBOR US + 2.09%), 2.20%, 02/15/37(a)(d)			1,530		1,438,146
Series 2020-SDAL, Class E, (1 mo. LIBOR US + 2.74%), 2.85%, 02/15/37(a)(d)			1,300		1,189,441
WFRBS Commercial Mortgage Trust, Series 2014-C24, Class B, 4.20%, 11/15/47(d)			770		775,237
					748,211,597
Interest Only Collateralized Mortgage Obligations — 0.0%
Seasoned Credit Risk Transfer Trust, Series 2017-3, Class BIO, 0.00%, 07/25/56(a)(d)			3,210		455,595
Voyager OPTONE Delaware Trust, Series 2009-1, Class SAA7, 6.72%, 02/25/38(a)(d)			13,612		4,133,095
					4,588,690
Interest Only Commercial Mortgage-Backed Securities — 0.2%
245 Park Avenue Trust, Series 2017-245P, Class XA, 0.15%, 06/05/37(a)(d)			13,000		136,106
Banc of America Commercial Mortgage Trust
Series 2017-BNK3, Class XB, 0.63%, 02/15/50(d)			11,850		397,171
Series 2017-BNK3, Class XD, 1.28%, 02/15/50(a)(d)			5,000		308,200
BANK
Series 2019-BN20, Class XA, 0.84%, 09/15/62(d)			11,491		675,368
Series 2019-BN20, Class XB, 0.36%, 09/15/62(d)			39,279		1,123,183
Barclays Commercial Mortgage Trust, Series 2019-C3, Class XA, 1.34%, 05/15/52(d)			9,935		893,331
BBCMS Mortgage Trust
Series 2015-SRCH, Class XA, 0.95%, 08/10/35(a)(d)			17,427		800,426
Series 2020-C7, Class XA, 1.63%, 04/15/53(d)			8,113		863,841
Series 2020-C7, Class XB, 0.99%, 04/15/53(d)			1,596		131,069
Benchmark Mortgage Trust Series 2019-B13, Class XA, 1.13%, 08/15/57(d)			58,087		4,233,843

72 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Interest Only Commercial Mortgage-Backed Securities (continued)
Benchmark Mortgage Trust
Series 2019-B9, Class XA, 1.04%, 03/15/52(d)	USD		13,366	$	906,471
Series 2020-B17, Class XB, 0.53%, 03/15/53(b)(d)			7,100		283,327
Series 2020-B20, Class XA, 1.63%, 10/15/53(d)			23,189		2,510,238
Series 2020-B21, Class XA, 1.46%, 12/17/53(d)			9,326		1,007,436
Series 2021-B23, Class XA, 1.28%, 02/15/54(d)			27,631		2,661,165
CFCRE Commercial Mortgage Trust
Series 2016-C3, Class XD, 1.70%, 01/10/48(a)(d)			5,497		395,484
Series 2016-C4, Class XB, 0.71%, 05/10/58(d)			5,810		196,785
Citigroup Commercial Mortgage Trust, Series 2020-420K, Class X, 0.80%, 11/10/42(a)(b)(d)			46,500		3,276,855
Commercial Mortgage Pass-Through Certificates
Series 2013-CR6, Class XA, 1.01%, 03/10/46(d)			16,166		166,478
Series 2015-3BP, Class XA, 0.06%, 02/10/35(a)(d)			150,000		541,500
Series 2015-CR25, Class XA, 0.83%, 08/10/48(d)			4,653		143,191
Series 2018-COR3, Class XD, 1.75%, 05/10/51(a)(d)			3,200		317,798
CSAIL Commercial Mortgage Trust
Series 2017-CX10, Class XB, 0.13%, 11/15/50(d)			12,490		179,977
Series 2019-C16, Class XA, 1.56%, 06/15/52(d)			30,626		3,060,202
Series 2019-C17, Class XA, 1.37%, 09/15/52(d)			26,732		2,327,660
Series 2019-C17, Class XB, 0.56%, 09/15/52(d)			19,090		746,465
DBGS Mortgage Trust, Series 2019-1735, Class X, 0.29%, 04/10/37(a)(d)			21,535		483,891
Deutsche Bank JPMorgan Mortgage Trust, Series 2017-C6, Class XD, 1.00%, 06/10/50(d)			5,780		282,873
FREMF Mortgage Trust, Series 2019-KW08, Class X2A, 0.10%, 01/25/29(a)			154,166		888,290
GS Mortgage Securities Corp. II, Series 2005- ROCK, Class X1, 0.21%, 05/03/32(a)(d)			21,000		224,494
GS Mortgage Securities Trust
Series 2019-GSA1, Class XA, 0.83%, 11/10/52(d)			14,667		866,937
Series 2020-GSA2, Class XA, 1.74%, 12/12/53(a)(d)			37,435		4,767,279
JPMBB Commercial Mortgage Securities Trust
Series 2014-C22, Class XA, 0.83%, 09/15/47(d)			1,917		45,462
Series 2014-C23, Class XA, 0.63%, 09/15/47(d)			28,385		504,447
Series 2015-C29, Class XA, 0.65%, 05/15/48(d)			1,915		44,057
JPMDB Commercial Mortgage Securities Trust, Series 2016-C4, Class XC, 0.75%, 12/15/49(a)(d)			4,940		171,846

Security		Par (000)		Value
Interest Only Commercial Mortgage-Backed Securities (continued)
JPMorgan Chase Commercial Mortgage Securities Trust
Series 2013-LC11, Class XB, 0.51%, 04/15/46(d)	USD		4,570	$	47,367
Series 2016-JP3, Class XC, 0.75%, 08/15/49(a)(d)			13,040		443,450
Ladder Capital Commercial Mortgage Trust, Series 2013-GCP, Class XA, 1.17%, 02/15/36(a)(d)			3,835		252,296
LSTAR Commercial Mortgage Trust, Series 2017-5, Class X, 0.99%, 03/10/50(a)(d).			3,230		94,695
Morgan Stanley Bank of America Merrill Lynch Trust
Series 2014-C19, Class XF, 1.21%, 12/15/47(a)(d)			4,370		170,517
Series 2015-C26, Class XD, 1.34%, 10/15/48(a)(d)			4,490		248,791
Morgan Stanley Capital I Trust
Series 2016-UBS9, Class XD, 1.61%, 03/15/49(a)(d)			13,984		981,677
Series 2017-H1, Class XD, 2.20%, 06/15/50(a)(d)			3,293		355,018
Series 2019-H6, Class XB, 0.72%, 06/15/52(d)			23,510		1,168,485
Series 2019-L2, Class XA, 1.03%, 03/15/52(d)			8,818		596,192
Olympic Tower Mortgage Trust, Series 2017-OT, Class XA, 0.38%, 05/10/39(a)(d)			36,697		806,967
One Market Plaza Trust
Series 2017-1MKT, Class XCP, 0.09%, 02/10/32(a)(d)			53,230		72,393
Series 2017-1MKT, Class XNCP, 0.00%, 02/10/32(a)(b)(d)			10,646		106
UBS Commercial Mortgage Trust
Series 2019-C17, Class XA, 1.49%, 10/15/52(d)			32,472		3,172,847
Series 2019-C18, Class XA, 1.04%, 12/15/52(d)			35,584		2,338,008
Wells Fargo Commercial Mortgage Trust
Series 2015-NXS4, Class XA, 1.04%, 12/15/48(d)			2,353		94,719
Series 2016-BNK1, Class XD, 1.26%, 08/15/49(a)(d)			4,420		247,122
Series 2019-C50, Class XA, 1.42%, 05/15/52(d)			24,814		2,163,729
Series 2020-C58, Class XA, 1.89%, 07/15/53(d)			17,410		2,415,885
					52,233,410
Principal Only Collateralized Mortgage Obligations — 0.0%
Seasoned Credit Risk Transfer Trust, Series 2017-3, Class B, 0.00%, 07/25/56(a)(m)			1,554		247,306
Total Non-Agency Mortgage-Backed Securities — 5.9% (Cost: $1,246,862,973)					1,243,708,579
Preferred Securities
Capital Trusts — 0.7%
Banks — 0.3%
Banco Industrial SA, 4.88%(a)			960		984,600
Banco Mercantil del Norte SA, 6.88%(a)(l)			920		939,550
Bangkok Bank PCL, 5.00%(l)			300		315,281

MASTER  PORTFOLIO   SCHEDULE   OF   INVESTMENTS 73

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Banks (continued)
Bank of America Corp., Series FF, 5.88%(l)	USD		10,500	$	11,452,035
Bank of East Asia Ltd., 5.83%(l)			510		546,816
Burgan Bank SAK, 5.75%(l)			1,729		1,711,170
Chong Hing Bank Ltd., 5.70%(l)			250		261,406
Citigroup, Inc.
3.88%(l)			6,991		6,958,352
Series W, 4.00%(l)			18,332		18,510,737
Emirates NBD Bank PJSC
6.13%(l)			3,865		4,115,017
6.13%(l)			750		814,219
HSBC Holdings PLC, 4.70%(l)			8,040		7,919,400
Kasikornbank PCL, 5.28%(l)			400		420,625
Kookmin Bank, 4.35%(l)			1,307		1,377,660
Lehman Brothers Holdings Capital Trust VII, 5.86%(b)(g)(k)(l)			1,888		—
Nanyang Commercial Bank Ltd., 5.00%(l)			200		204,937
NBK Tier 1 Financing Ltd., 3.63%(a)(l)			3,798		3,775,174
Rizal Commercial Banking Corp., 6.50%(l)			200		207,375
Shinhan Financial Group Co. Ltd., 5.88%(l)			214		231,120
Woori Bank, 4.25%(l)			200		209,000
					60,954,474
Capital Markets — 0.4%
Bank of New York Mellon Corp.
3.70%(l)			2,900		2,983,520
Series E, (3 mo. LIBOR US + 3.42%), 3.61%(d)(l)			4,380		4,379,051
Series F, 4.63%(l)			9,722		10,256,710
Charles Schwab Corp., Series H, 4.00%(l)			12,500		12,287,500
State Street Corp.
Series F, (3 mo. LIBOR US + 3.60%), 3.78%(d)(l)			1,338		1,341,680
Series H, 5.63%(l)			19,655		20,663,301
UBS Group AG
4.38%(a)(l)			2,280		2,249,220
7.00%(a)(l)			15,350		16,860,286
					71,021,268
Commercial Services & Supplies — 0.0%
King Talent Management Ltd., 5.60%(l)			600		527,625
Insurance — 0.0%
Heungkuk Life Insurance Co. Ltd., 4.48%(l)			1,000		1,008,437
KDB Life Insurance Co. Ltd., 7.50%(l)			900		904,781
Tongyang Life Insurance Co. Ltd., 5.25%(l)			950		982,063
					2,895,281
Machinery — 0.0%
Weichai International Hong Kong Energy Group Co. Ltd., 3.75%(l)			278		282,344
Real Estate Management & Development — 0.0%
MAF Global Securities Ltd., 5.50%(l)			1,341		1,353,572
Total Preferred Securities — 0.7% (Cost: $134,744,445)					137,034,564
		Shares
Rights
Diversified Financial Services — 0.0%
Crown PropTech Acquisitions(b)			214,560		321,840
Total Rights — 0.0% (Cost: $321,840)					321,840

Security		Par (000)		Value
U.S. Government Sponsored Agency Securities
Agency Obligations — 0.0%
Fannie Mae, 6.63%, 11/15/30	USD		1,450	$	2,068,864
Collateralized Mortgage Obligations — 0.2%
Fannie Mae, Series 2003-W5, Class A, (1 mo. LIBOR US + 0.11%), 0.34%, 04/25/33(d)			1		1,368
Freddie Mac
Series 2015-DN1, Class B, (1 mo. LIBOR US + 11.50%), 11.61%, 01/25/25(d)			487		508,522
Series 2015-HQ2, Class B, (1 mo. LIBOR US + 7.95%), 8.06%, 05/25/25(d)			520		530,033
Series 2017-DNA2, Class B1, (1 mo. LIBOR US + 5.15%), 5.26%, 10/25/29(d)			590		632,869
Series 2017-DNA3, Class B1, (1 mo. LIBOR US + 4.45%), 4.56%, 03/25/30(d)			1,860		1,930,139
Series 2017-HRP1, Class M2, (1 mo. LIBOR US + 2.45%), 2.56%, 12/25/42(d)			484		478,820
Series 2020-DNA4, Class M2, (1 mo. LIBOR US + 3.75%), 3.86%, 08/25/50(a)(d)			3,520		3,551,426
Series 2020-DNA5, Class B1, (Secured Overnight Financing Rate (30-day) + 4.80%), 4.82%, 10/25/50(a)(d)			990		1,027,770
Series 2020-DNA6, Class B1, (Secured Overnight Financing Rate (30-day) + 3.00%), 3.02%, 12/25/50(a)(d)			3,640		3,583,341
Series 2020-HQA5, Class B1, (Secured Overnight Financing Rate (30-day) + 4.00%), 4.02%, 11/25/50(a)(d)			2,410		2,467,320
Series 2021-DNA1, Class B1, (Secured Overnight Financing Rate (30-day) + 2.65%), 2.67%, 01/25/51(a)(d)			8,510		8,190,849
Series 2021-DNA1, Class B2, (Secured Overnight Financing Rate (30-day) + 4.75%), 4.77%, 01/25/51(a)(d)			5,220		4,871,343
Series 2021-DNA2, Class B1, (Secured Overnight Financing Rate (30-day) + 3.40%), 3.42%, 08/25/33(a)(d)			7,000		6,930,003
Series 2021-DNA2, Class B2, (Secured Overnight Financing Rate (30-day) + 6.00%), 6.02%, 08/25/33(a)(d)			6,320		6,130,699
Series 2021-HQA1, Class B1, (Secured Overnight Financing Rate (30-day) + 3.00%), 3.02%, 08/25/33(a)(d)			8,632		8,524,191
Series 2021-HQA1, Class B2, (Secured Overnight Financing Rate (30-day) + 5.00%), 5.02%, 08/25/33(a)(d)			5,189		4,879,352
					54,238,045
Commercial Mortgage-Backed Securities — 0.0%
Fannie Mae, Series 2006-M2, Class A2A, 5.27%, 10/25/32(d)			648		710,982
Interest Only Collateralized Mortgage Obligations — 0.1%
Fannie Mae
Series 2020-32, Class PI, 4.00%, 05/25/50			11,910		1,887,633
Series 2020-73, Class AI, 2.00%, 10/25/50			6,792		636,643
Series 2020-96, Class IB, 3.00%, 01/25/51			6,660		914,599
Series 2021-3, Class JI, 2.50%, 02/25/51			10,130		1,221,986
Freddie Mac
Series 4940, Class PI, 4.00%, 07/25/49			5,483		700,299
Series 4995, Class BI, 4.50%, 06/25/50			5,411		815,022
Series 4999, Class QI, 4.00%, 05/25/50			5,634		955,761
Series 5014, Class DI, 4.00%, 09/25/50			3,931		587,191
Series 5018, Class CI, 4.50%, 10/25/50			5,429		990,067

74 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
Interest Only Collateralized Mortgage Obligations (continued)
Freddie Mac
Series 5020, Class IC, 2.00%, 10/25/50	USD		9,061	$	1,100,207
Series 5029, Class GI, 2.00%, 10/25/50			5,128		608,856
Series 5057, Class TI, 3.00%, 11/25/50			7,999		1,280,857
Series 5082, Class IW, 3.00%, 03/25/51			7,145		950,592
Ginnie Mae
Series 2020-144, Class IO, 2.50%, 09/20/50			9,400		1,243,050
Series 2020-146, Class DI, 2.50%, 10/20/50			7,350		889,540
Series 2020-151, Class MI, 2.50%, 10/20/50			38,350		4,894,359
Series 2020-175, Class DI, 2.50%, 11/20/50			2,665		350,621
Series 2020-185, Class MI, 2.50%, 12/20/50			8,839		1,235,766
Series 2021-15, Class GI, 3.50%, 01/20/51			5,361		760,621
					22,023,670
Interest Only Commercial Mortgage-Backed Securities — 0.1%
Freddie Mac
Series K099, Class X1, 0.89%, 09/25/29(d)			15,478		1,014,717
Series K110, Class X1, 1.70%, 04/25/30(d)			8,481		1,093,149
Series K111, Class X1, 1.57%, 05/25/30(d)			20,321		2,494,637
Series K121, Class X1, 1.03%, 10/25/30(d)			13,893		1,145,943
Series K122, Class X1, 0.88%, 11/25/30(d)			12,645		913,945
Series KL06, Class XFX, 1.36%, 12/25/29			6,710		625,057
Series KW09, Class X1, 0.80%, 05/25/29(d)			36,910		1,991,357
Ginnie Mae
Series 2012-23, Class IO, 0.18%, 06/16/53(d)			1,634		10,232
Series 2013-191, Class IO, 0.68%, 11/16/53(d)			2,494		49,616
Series 2013-30, Class IO, 0.65%, 09/16/53(d)			8,044		166,709
Series 2013-63, Class IO, 0.76%, 09/16/51(d)			10,582		309,872
Series 2013-78, Class IO, 0.57%, 10/16/54(d)			8,208		172,347
Series 2015-173, Class IO, 0.77%, 09/16/55(d)			4,431		162,317
Series 2015-22, Class IO, 0.60%, 03/16/55(d)			6,544		193,319
Series 2015-37, Class IO, 0.70%, 10/16/56(d)			1,195		47,525
Series 2015-48, Class IO, 0.62%, 02/16/50(d)			4,155		131,459
Series 2016-110, Class IO, 0.95%, 05/16/58(d)			4,084		228,208
Series 2016-113, Class IO, 1.15%, 02/16/58(d)			5,991		411,235
Series 2016-125, Class IO, 0.95%, 12/16/57(d)			6,171		343,368
Series 2016-128, Class IO, 0.87%, 09/16/56(d)			8,912		486,147
Series 2016-152, Class IO, 0.80%, 08/15/58(d)			6,234		342,127
Series 2016-165, Class IO, 0.88%, 12/16/57(d)			3,093		172,719
Series 2016-26, Class IO, 0.79%, 02/16/58(d)			22,200		945,573
Series 2016-36, Class IO, 0.81%, 08/16/57(d)			1,931		87,672
Series 2016-92, Class IO, 0.84%, 04/16/58(d)			3,154		151,856
Series 2016-96, Class IO, 0.90%, 12/16/57(d)			7,005		372,807
					14,063,913

Security		Par (000)		Value
Mortgage-Backed Securities — 58.5%
Fannie Mae Mortgage-Backed Securities
2.00%, 10/01/31 - 03/01/32	USD		11,900	$	12,241,063
2.50%, 09/01/27 - 12/01/50			142,641		149,400,567
3.00%, 04/01/28 - 08/01/50(q)			394,249		414,726,955
3.50%, 08/01/28 - 08/01/50			102,830		111,219,485
4.00%, 08/01/31 - 09/01/50			52,490		57,470,497
4.50%, 02/01/25 - 02/01/50			293,932		327,707,602
5.00%, 11/01/32 - 06/01/45			19,257		22,226,250
5.50%, 12/01/32 - 04/01/41			16,763		19,494,296
6.00%, 02/01/34 - 06/01/41			9,933		11,546,521
6.50%, 05/01/40			2,039		2,416,326
Freddie Mac Mortgage-Backed Securities
2.50%, 04/01/27 - 04/01/31			15,518		16,259,305
3.00%, 09/01/27 - 09/01/50			391,003		414,240,752
3.50%, 09/01/30 - 08/01/50			308,679		333,867,976
4.00%, 08/01/40 - 06/01/50			139,755		154,079,278
4.50%, 02/01/39 - 10/01/50			154,189		169,956,191
5.00%, 07/01/35 - 11/01/41			7,087		8,207,194
5.50%, 02/01/35 - 06/01/41			2,278		2,670,841
Ginnie Mae Mortgage-Backed Securities
2.00%, 04/15/51(r)			214,446		216,523,448
2.50%, 04/15/51(r)			246,423		254,258,483
3.00%, 12/20/44 - 04/15/51(r)			592,465		617,397,096
3.50%, 01/15/42 - 04/15/51(r)			297,259		316,102,659
4.00%, 04/20/39 - 04/15/51(r)			148,869		159,891,510
4.50%, 12/20/39 - 04/15/51(r)			62,481		68,068,441
5.00%, 04/15/33 - 04/15/51(r)			35,927		39,617,362
Uniform Mortgage-Backed Securities
1.50%, 04/01/36 - 04/01/51(r)			820,449		796,094,269
2.00%, 04/01/36 - 04/01/51(r)			3,105,152		3,105,665,973
2.50%, 04/01/36 - 04/01/51(r)			2,925,813		2,999,439,239
3.00%, 04/01/36 - 04/01/51(r)			608,062		634,182,418
3.50%, 04/01/36 - 04/01/51(r)			247,378		261,418,050
4.00%, 04/01/36 - 04/01/51(r)			513,802		551,218,011
4.50%, 04/01/51(r)			14,400		15,675,750
5.00%, 04/01/51(r)			42,159		46,705,091
					12,309,988,899
Total U.S. Government Sponsored Agency Securities — 58.9% (Cost: $12,416,397,225)					12,403,094,373
U.S. Treasury Obligations
U.S. Treasury Bonds
4.63%, 02/15/40			10,812		14,910,846
3.88%, 08/15/40			10,812		13,632,412
4.25%, 11/15/40			10,812		14,304,783
1.88%, 02/15/41 - 02/15/51			60,923		55,733,137
2.50%, 02/15/45			88,094		89,931,586
2.75%, 11/15/47			88,610		94,740,012
3.00%, 02/15/48(q)			88,094		98,751,309
U.S. Treasury Inflation Indexed Notes, 0.13%, 01/15/31(s)			282,557		304,141,994
U.S. Treasury Notes
1.75%, 07/15/22 - 11/15/29(e)			253,010		259,254,238
0.50%, 03/15/23 - 05/31/27			436,195		430,335,379
0.25%, 04/15/23			167,495		167,737,082
1.50%, 10/31/24 - 02/15/30			85,515		86,972,983
2.25%, 11/15/24 - 08/15/27			147,346		156,338,412
0.38%, 04/30/25			181,142		178,870,650
0.63%, 03/31/27			60,677		58,664,704

MASTER    PORTFOLIO   SCHEDULE   OF   INVESTMENTS 75

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio (Percentages shown are based on Net Assets)

Security		Par (000)		Value
U.S. Treasury Obligations (continued)
2.25%, 11/15/24 - 08/15/27	USD		147,346	$	156,338,412
2.38%, 05/15/27			20,160		21,546,787
1.63%, 08/15/29			31,559		31,671,183
Total U.S. Treasury Obligations — 9.9% (Cost: $2,176,109,245)					2,077,537,497
		Shares
Warrants(g)
Diversified Financial Services — 0.0%
Climate Change Crisis Real Impact I Acquisition Corp. (Issued/Exercisable 11/10/20, 1 Share for 1 Warrant, Expires 09/15/25, Strike Price USD 11.50)			118,340		385,788
Decarbonization Plus Acquisition Corp. (Issued/Exercisable 12/10/20, 1 Share for 1 Warrant, Expires 10/02/25, Strike Price USD 11.50)			196,188		366,872
dMY Technology Group, Inc. II (Issued/Exercisable 09/25/20, 1 Share for 1 Warrant, Expires 07/29/27, Strike Price USD 11.50)			319,200		1,342,555
Dragoneer Growth Opportunities Corp. (Issued/Exercisable 08/14/20, 1 Share for 1 Warrant, Expires 08/14/25, Strike Price USD 11.50)			53,462		85,005
Jaws Acquisition Corp. (Issued/Exercisable 07/06/20, 1 Share for 1 Warrant, Expires 07/06/25, Strike Price USD 11.50)			98,960		314,693
KINS Technology Group, Inc. (Issued/Exercisable 10/31/25, 1 Share for 1 Warrant, Expires 10/31/25, Strike Price USD 11.50)(b)			469,648		380,415
Lakestar Spac I SE (Issued/Exercisable 02/22/21, 1 Share for 1 Warrant, Expires 12/31/25, Strike Price EUR 0.00)			35,820		44,106
Rotor Acquisition Corp. (Issued/Exercisable 01/31/26, 1 Share for 1 Warrant, Expires 01/31/26, Strike Price USD 11.50)(b)			78,620		78,620
Tortoise Acquisition Corp. II (Issued/Exercisable 10/22/20, 1 Share for 1 Warrant, Expires 06/14/27, Strike Price USD 11.50)			121,900		398,613
TPG Pace Beneficial Finance Corp. (Issued/Exercisable 11/17/20, 1 Share for 1 Warrant, Expires 10/09/27, Strike Price USD 11.50)			52,890		395,088
					3,791,755
Oil, Gas & Consumable Fuels — 0.0%
California Resources Corp. (Issued/Exercisable 10/27/24, 1 Share for 1 Warrant, Expires 10/27/24, Strike Price USD 36.00)			4,466		20,320
Chesapeake Energy Corp. (Issued/Exercisable 02/09/21, 1 Share for 1 Warrant, Expires 02/09/26, Strike Price USD 36.18)			7,534		126,571
SM Energy Co. (Issued/Exercisable 06/30/23, 1 Share for 1 Warrant, Expires 06/30/23, Strike Price USD 0.01)			51,102		836,029
					982,920

Security		Shares		Value
Real Estate Management & Development — 0.0%
Target Hospitality Corp. (Issued/Exercisable 03/05/18, 1 Share for 1 Warrant, Expires 03/15/24, Strike Price USD 11.50)			8,280	$	1,408
Total Warrants — 0.0% (Cost: $12,155,835)					4,776,083
Total Long-Term Investments — 134.7% (Cost: $28,326,182,676)					28,369,532,902
Short-Term Securities
Money Market Funds — 9.6%
BlackRock Liquidity Funds, T-Fund, Institutional Class, 0.01%(p)(t)			1,842,635,593		1,842,635,593
SL Liquidity Series, LLC, Money Market Series, 0.16%(p)(t)(u)			166,017,227		166,056,420
Total Short-Term Securities — 9.6% (Cost: $2,008,692,013)					2,008,692,013
Options Purchased — 0.8%
(Cost: $56,979,711)					160,218,377
Total Investments Before Options Written and TBA Sale Commitments — 145.1% (Cost: $30,391,854,400)					30,538,443,292
		Par (000)
TBA Sale Commitments(r)
Mortgage-Backed Securities — (33.3)%
Ginnie Mae Mortgage-Backed Securities
3.00%, 04/15/51	USD		13,761		(14,335,629	)
3.50%, 04/15/51			2,967		(3,130,881	)
4.00%, 04/15/51			2,836		(3,027,430	)
4.50%, 04/15/51			2,671		(2,888,854	)
Uniform Mortgage-Backed Securities
1.50%, 04/01/51			1,332,515		(1,286,366,678	)
2.00%, 04/01/36 - 04/01/51			2,998,057		(2,993,635,936	)
2.50%, 04/01/36 - 04/01/51			1,808,430		(1,855,011,345	)
3.00%, 04/01/36 - 04/01/51			536,206		(558,575,397	)
3.50%, 04/01/51			22,212		(23,464,028	)
4.00%, 04/01/36 - 04/01/51			225,695		(242,110,430	)
4.50%, 04/01/51			19,795		(21,548,713	)
Total TBA Sale Commitments — (33.3)% (Proceeds: $(7,054,477,396))					(7,004,095,321	)
Options Written — (0.5)% (Premiums Received: $(37,897,867))					(102,183,528	)
Total Investments Net of Options Written and TBA Sale Commitments — 111.3% (Cost: $23,299,479,137)					23,432,164,443
Liabilities in Excess of Other Assets — (11.3)%					(2,375,431,309	)
Net Assets — 100.0%				$	21,056,733,134

^(a)  Security exempt from registration pursuant to Rule 144A under the Securities Act of 1933, as amended. These securities may be resold in transactions exempt from registration to qualified institutional investors.

^(b)  Security is valued using significant unobservable inputs and is classified as Level 3 in the fair value hierarchy.

^(c)  Step-up bond that pays an initial coupon rate for the first period and then a higher coupon rate for the following periods. Rate as of period end.

^(d)  Variable rate security. Interest rate resets periodically. The rate shown is the effective interest rate as of period end. Security description also includes the reference rate and spread if published and available.

76 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

^(e)  All or a portion of the security has been pledged and/or segregated as collateral in connection with outstanding exchange-traded options written.

^(f)  Restricted security as to resale, excluding 144A securities. The Master Portfolio held restricted securities with a current value of $11,632,956, representing 0.1% of its net assets as of period end, and an original cost of $12,949,329.

^(g)  Non-income producing security.

^(h)  All or a portion of this security is on loan.

⁽ⁱ⁾  Payment-in-kind security which may pay interest/dividends in additional par/shares and/or in cash. Rates shown are the current rate and possible payment rates.

^(j)  Convertible security.

^(k)  Issuer filed for bankruptcy and/or is in default.

^(l)  Perpetual security with no stated maturity date.

^(m)  Zero-coupon bond.

⁽ⁿ⁾  Issuer is a U.S. branch of a foreign domiciled bank.

^(o)  Represents an unsettled loan commitment at period end. Certain details associated with this purchase are not known prior to the settlement date, including coupon rate.

^(p)  Affiliate of the Master Portfolio.

^(q)  All or a portion of the security has been pledged as collateral in connection with outstanding TBA commitments.

^(r) Represents or includes a TBA transaction.

^(s)  All or a portion of the security has been pledged as collateral in connection with outstanding OTC derivatives.

^(t)  Annualized 7-day yield as of period end.

^(u)  All or a portion of this security was purchased with the cash collateral from loaned securities.

Affiliates

Investments in issuers considered to be affiliate(s) of the Master Portfolio during the six months ended March 31, 2021 for purposes of Section 2(a)(3) of the Investment Company Act of 1940, as amended, were as follows:

Affiliated Issuer	Value at 09/30/20		Purchases at Cost			Proceeds from Sale			Net Realized Gain (Loss)			Change in Unrealized Appreciation (Depreciation)				Value at 03/31/21		Par/Shares Held at 03/31/21		Income			Capital   Gain   Distributions   from Underlying   Funds
BlackRock Capital Finance LP, Series 1997- R2, Class AP	$	3,188	$	—		$	—		$			—	$	(333	)	$	2,855		3,373	$	—			$	—
BlackRock Liquidity Funds, T-Fund, Institutional Class		178,500,805		1,664,134,788	(a)		—			—				—			1,842,635,593		1,842,635,593		83,419				—
iShares 0-5 Year High Yield Corporate Bond ETF(b)		—		345,143			(347,921	)		2,778				—			—		—		3,316				—
iShares iBoxx High Yield Corporate Bond ETF(b)		127,840,947		98,729,420			(235,133,109	)		7,937,077				625,665			—		—		4,174,834				—
SL Liquidity Series, LLC, Money Market Series		56,783,936		109,292,919	(a)		—			(20,490	)			55			166,056,420		166,017,227		306,403	(c)			—
									$	7,919,365			$	625,387		$	2,008,694,868			$	4,567,972			$	—

^(a)  Represents net shares purchased (sold).

^(b)  As of period end, the entity is no longer held by the Master Portfolio.

^(c)  All or a portion represents securities lending income earned from the reinvestment of cash collateral from loaned securities, net of fees and collateral investment expenses, and other payments to and from borrowers of securities.

For Master Portfolio compliance purposes, the Master Portfolio’s industry classifications refer to one or more of the industry sub-classifications used by one or more widely recognized market indexes or rating group indexes, and/or as defined by the investment adviser. These definitions may not apply for purposes of this report, which may combine such industry sub-classifications for reporting ease.

MASTER    PORTFOLIO    SCHEDULE   OF    INVESTMENTS 77

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Derivative Financial Instruments Outstanding as of Period End

Futures Contracts

Description	Number of Contracts		Expiration Date		Notional Amount (000)		Value/ Unrealized Appreciation (Depreciation)
Long Contracts
Euro-Bobl		4,913		06/08/21	$	778,260	$	218,239
Euro-Bund		383		06/08/21		76,929		(259,951	)
NASDAQ 100 E-Mini Index		2		06/18/21		524		15,020
U.S. Treasury Bonds (30 Year)		5,841		06/21/21		904,442		(12,614,725	)
U.S. Treasury Notes (10 Year)		4,289		06/21/21		562,060		(3,815,432	)
U.S. Ultra Treasury Bonds		5,658		06/21/21		1,029,049		(39,399,369	)
U.S. Treasury Notes (2 Year)		5,469		06/30/21		1,207,239		(940,892	)
U.S. Treasury Notes (5 Year)		10,024		06/30/21		1,237,494		(6,437,576	)
Canadian Bankers Acceptance		2,055		06/13/22		406,192		(191,677	)
Canadian Bankers Acceptance		1,842		09/19/22		363,449		(507,572	)
Euro Dollar		150		09/18/23		37,116		(3,979	)
Three Month Sterling		1,522		12/20/23		260,482		(101,866	)
								(64,039,780	)
Short Contracts
Euro-BTP Italian Government Bond		206		06/08/21		36,070		139,982
Euro-Buxl		1,264		06/08/21		305,412		1,735,808
Euro-OAT		40		06/08/21		7,597		11,843
Canadian Bankers Acceptance		2,055		06/14/21		406,949		(135,391	)
Japanese 10-Year Bonds		38		06/14/21		51,877		(34,299	)
E-Mini S&P 500 Index		965		06/18/21		191,427		(978,931	)
Canadian Government Bonds (10 Year)		503		06/21/21		55,543		517,721
Canadian Government Bonds (5 Year)		105		06/21/21		10,517		(25,494	)
U.S. Ultra Treasury Notes (10 Year)		11,139		06/21/21		1,602,624		28,296,546
10 Year U.K. Gilt		2,006		06/28/21		352,847		1,808,994
Canadian Bankers Acceptance		1,842		09/13/21		364,695		(85,912	)
Euro Dollar		12,804		09/16/24		3,145,943		11,048,389
Three Month Sterling		1,522		12/18/24		259,813		187,036
								42,486,292
							$	(21,553,488	)

Forward Foreign Currency Exchange Contracts

Currency Purchased		Currency Sold		Counterparty	Settlement Date		Unrealized Appreciation (Depreciation)
BRL	12,075,291	USD	2,083,000	UBS AG		04/05/21		$   61,688
USD	2,076,000	BRL	11,488,584	Citibank N.A.		04/05/21		35,517
USD	2,076,000	BRL	11,488,584	Citibank N.A.		04/05/21		35,517
USD	4,151,000	BRL	22,571,478	Citibank N.A.		04/05/21		142,088
USD	4,239,000	BRL	23,049,986	Citibank N.A.		04/05/21		145,100
USD	2,083,000	BRL	11,544,194	Citibank N.A.		04/05/21		32,640
USD	1,038,000	COP	3,765,864,000	BNP Paribas S.A.		04/05/21		9,623
USD	2,076,000	COP	7,531,728,000	BNP Paribas S.A.		04/05/21		19,247
USD	4,184,000	RUB	314,092,880	BNP Paribas S.A.		04/05/21		32,624
USD	2,093,000	RUB	156,765,700	Citibank N.A.		04/05/21		21,023
USD	3,139,000	RUB	235,111,100	Citibank N.A.		04/05/21		31,529
CAD	37,522,163	USD	29,745,099	JPMorgan Chase Bank N.A.		04/12/21		113,355
GBP	21,598,415	USD	29,745,099	JPMorgan Chase Bank N.A.		04/12/21		31,685
USD	29,745,099	AUD	39,052,783	Deutsche Bank AG		04/12/21		80,527
USD	26,026,962	AUD	34,171,186	Deutsche Bank AG		04/12/21		70,461
USD	29,745,099	EUR	25,305,674	Deutsche Bank AG		04/12/21		61,749
USD	26,026,962	EUR	22,142,465	Deutsche Bank AG		04/12/21		54,030
USD	29,745,099	GBP	21,558,934	Deutsche Bank AG		04/12/21		22,745
USD	26,026,962	GBP	18,864,068	Deutsche Bank AG		04/12/21		19,902
EUR	2,650,000	JPY	341,434,771	Barclays Bank PLC		04/14/21		24,461

78 2 0 2 1   BLACK ROCK   SEMI - ANNUAL  REPORT  TO  SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Forward Foreign Currency Exchange Contracts (continued)

Currency Purchased		Currency Sold		Counterparty	Settlement Date			Unrealized Appreciation (Depreciation)
EUR	2,650,000	JPY	341,434,771	Barclays Bank PLC		04/14/21		$	24,461
JPY	344,480,310	EUR	2,650,000	JPMorgan Chase Bank N.A.		04/14/21			3,049
JPY	344,480,310	EUR	2,650,000	JPMorgan Chase Bank N.A.		04/14/21			3,049
MXN	108,521,624	USD	5,264,000	Citibank N.A.		04/14/21			37,346
RUB	239,222,160	USD	3,132,000	Bank of America N.A.		04/14/21			26,054
USD	3,559,854	MXN	72,784,063	HSBC Bank PLC		04/14/21			4,309
USD	614,146	MXN	12,560,470	JPMorgan Chase Bank N.A.		04/14/21			560
USD	2,074,000	RUB	153,144,160	Citibank N.A.		04/14/21			52,291
USD	2,100,000	RUB	155,295,000	JPMorgan Chase Bank N.A.		04/14/21			49,897
USD	2,087,000	ZAR	30,826,879	Citibank N.A.		04/14/21			2,451
USD	398,000	ZAR	5,883,232	Morgan Stanley & Co. International PLC		04/14/21			169
ZAR	77,669,946	USD	5,220,000	Bank of America N.A.		04/14/21			32,130
ZAR	93,999,688	USD	6,250,000	Bank of America N.A.		04/14/21			106,366
ZAR	63,198,056	USD	4,211,000	BNP Paribas S.A.		04/14/21			62,524
ZAR	104,710,545	USD	7,060,000	Citibank N.A.		04/14/21			20,646
MXN	9,447,284	USD	455,672	Bank of America N.A.		04/15/21			5,783
MXN	54,885,895	USD	2,655,328	Citibank N.A.		04/15/21			25,590
MXN	86,111,637	USD	4,166,000	Citibank N.A.		04/15/21			40,148
RUB	237,344,412	USD	3,111,000	BNP Paribas S.A.		04/15/21	��		21,852
USD	7,037,517	EUR	5,873,000	Barclays Bank PLC		04/15/21			148,107
USD	3,787,773	EUR	3,161,000	Barclays Bank PLC		04/15/21			79,715
USD	2,064,155	RUB	153,139,659	BNP Paribas S.A.		04/15/21			42,772
USD	2,368,633	RUB	175,728,882	BNP Paribas S.A.		04/15/21			49,081
USD	1,376,831	RUB	102,188,397	Citibank N.A.		04/15/21			27,985
USD	1,199,845	RUB	89,052,496	Citibank N.A.		04/15/21			24,387
USD	2,088,000	TRY	15,610,759	Bank of America N.A.		04/15/21			219,245
USD	3,810,000	TRY	28,956,000	Citibank N.A.		04/15/21			343,693
ZAR	62,561,092	USD	4,168,000	UBS AG		04/15/21			61,875
BRL	5,815,499	USD	1,023,495	Deutsche Bank AG		05/04/21			7,553
BRL	11,735,248	USD	2,062,905	Morgan Stanley & Co. International PLC		05/04/21			17,673
RUB	128,834,594	USD	1,685,214	Credit Suisse International		05/19/21			8,176
RUB	129,589,238	USD	1,691,037	Credit Suisse International		05/19/21			12,272
RUB	172,628,720	USD	2,259,331	HSBC Bank PLC		05/19/21			9,685
RUB	256,915,755	USD	3,360,177	Morgan Stanley & Co. International PLC		05/19/21			16,700
RUB	129,589,238	USD	1,689,031	Morgan Stanley & Co. International PLC		05/19/21			14,277
USD	1,783,507	RUB	132,684,034	Bank of America N.A.		05/19/21			39,521
USD	43,575,603	RUB	3,242,351,689	Citibank N.A.		05/19/21			958,437
USD	1,768,995	RUB	131,867,987	HSBC Bank PLC		05/19/21			35,735
USD	1,784,416	RUB	132,803,339	HSBC Bank PLC		05/19/21			38,861
USD	3,564,330	RUB	265,487,373	HSBC Bank PLC		05/19/21			74,789
USD	3,562,944	RUB	265,368,068	HSBC Bank PLC		05/19/21			74,971
USD	1,782,370	RUB	132,624,381	HSBC Bank PLC		05/19/21			39,168
USD	2,123,091	RUB	157,644,818	HSBC Bank PLC		05/19/21			51,022
IDR	77,449,000,000	USD	5,304,726	HSBC Bank PLC		05/24/21			5,080
USD	127,213,072	CNH	826,344,310	HSBC Bank PLC		05/24/21			1,852,289
USD	258,280	EUR	212,208	Bank of America N.A.		05/24/21			9,139
USD	2,425,557	EUR	2,003,989	Morgan Stanley & Co. International PLC		05/24/21			72,790
USD	5,974,231	IDR	86,847,997,508	Barclays Bank PLC		05/24/21			20,042
USD	23,691,985	IDR	337,089,555,370	JPMorgan Chase Bank N.A.		05/24/21			581,549
MXN	131,901,375	USD	6,139,031	Citibank N.A.		05/26/21			274,304
MXN	105,799,075	USD	4,946,843	HSBC Bank PLC		05/26/21			197,341
GBP	30,013,548	EUR	35,010,000	BNP Paribas S.A.		06/16/21			262,953
GBP	22,893,241	EUR	26,510,000	BNP Paribas S.A.		06/16/21			428,862
GBP	30,444,458	EUR	35,650,000	BNP Paribas S.A.		06/16/21			105,388
GBP	10,495,000	USD	14,456,170	UBS AG		06/16/21			15,700
USD	2,934,128	AUD	3,785,000	Barclays Bank PLC		06/16/21			58,275
USD	13,021,309	CAD	16,243,000	BNP Paribas S.A.		06/16/21			94,981
USD	277,160	CNH	1,819,112	Bank of America N.A.		06/16/21			1,671
USD	276,345	CNH	1,815,000	BNP Paribas S.A.		06/16/21			1,478
USD	329,892,239	CNH	2,177,123,830	Standard Chartered Bank		06/16/21			185,016
USD	77,743,576	CNH	513,068,730	Standard Chartered Bank		06/16/21			43,602
USD	4,420,522	EUR	3,707,621	Bank of America N.A.		06/16/21			65,457

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 79

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Forward Foreign Currency Exchange Contracts (continued)

Currency Purchased		Currency Sold		Counterparty	Settlement Date		Unrealized Appreciation (Depreciation)
USD	38,149,518	EUR	32,010,000	Bank of America N.A.		06/16/21	$	549,765
USD	39,625,195	EUR	33,608,016	Bank of America N.A.		06/16/21		148,372
USD	6,219,570	EUR	5,182,000	Bank of Montreal		06/16/21		132,662
USD	2,179,623	EUR	1,842,000	Bank of Montreal		06/16/21		15,964
USD	2,098,820	EUR	1,781,000	Bank of Montreal		06/16/21		6,812
USD	5,113,077	EUR	4,274,000	Barclays Bank PLC		06/16/21		92,729
USD	229,434,474	EUR	192,550,000	BNP Paribas S.A.		06/16/21		3,260,389
USD	41,327,211	EUR	34,587,000	BNP Paribas S.A.		06/16/21		700,449
USD	11,809,293	EUR	9,905,000	Citibank N.A.		06/16/21		174,630
USD	6,719,945	EUR	5,623,000	JPMorgan Chase Bank N.A.		06/16/21		115,027
USD	26,035,400	EUR	21,975,000	JPMorgan Chase Bank N.A.		06/16/21		223,011
USD	2,147,670	EUR	1,807,000	State Street Bank and Trust Co.		06/16/21		25,123
USD	17,905,281	EUR	14,906,000	State Street Bank and Trust Co.		06/16/21		396,318
USD	3,446,912	EUR	2,890,000	UBS AG		06/16/21		52,245
USD	2,587,385	HKD	20,084,449	HSBC Bank PLC		06/16/21		3,408
USD	4,412,244	JPY	479,779,000	Bank of New York Mellon		06/16/21		76,014
USD	5,360,000	JPY	584,630,744	JPMorgan Chase Bank N.A.		06/16/21		76,123
USD	2,651,319	JPY	288,419,026	Morgan Stanley & Co. International PLC		06/16/21		44,596
USD	16,669,941	JPY	1,816,408,000	Morgan Stanley & Co. International PLC		06/16/21		253,295
								14,582,735
BRL	12,068,973	USD	2,163,000	BNP Paribas S.A.		04/05/21		(19,434	)
BRL	22,798,632	USD	4,152,000	Citibank N.A.		04/05/21		(102,743	)
BRL	17,490,595	USD	3,126,000	Citibank N.A.		04/05/21		(19,502	)
BRL	17,242,025	USD	3,101,000	Deutsche Bank AG		04/05/21		(38,650	)
COP	7,515,120,000	USD	2,076,000	JPMorgan Chase Bank N.A.		04/05/21		(23,782	)
COP	3,757,560,000	USD	1,038,000	JPMorgan Chase Bank N.A.		04/05/21		(11,891	)
RUB	231,877,930	USD	3,139,000	UBS AG		04/05/21		(74,262	)
RUB	231,877,930	USD	3,139,000	UBS AG		04/05/21		(74,262	)
RUB	229,094,040	USD	3,111,000	UBS AG		04/05/21		(83,057	)
RUB	229,094,040	USD	3,111,000	UBS AG		04/05/21		(83,057	)
USD	1,045,000	COP	3,841,420,000	Citibank N.A.		04/05/21		(4,009	)
USD	2,090,000	COP	7,682,840,000	Citibank N.A.		04/05/21		(8,019	)
USD	3,111,000	RUB	237,058,200	BNP Paribas S.A.		04/05/21		(22,206	)
AUD	38,983,227	USD	29,745,099	JPMorgan Chase Bank N.A.		04/12/21		(133,362	)
EUR	25,278,469	USD	29,745,099	Deutsche Bank AG		04/12/21		(93,659	)
USD	29,745,099	CAD	37,385,038	Deutsche Bank AG		04/12/21		(4,237	)
USD	26,026,962	CAD	32,711,909	Deutsche Bank AG		04/12/21		(3,707	)
CLP	2,242,941,060	USD	3,139,000	Deutsche Bank AG		04/14/21		(25,382	)
CLP	2,242,941,060	USD	3,139,000	Deutsche Bank AG		04/14/21		(25,382	)
MXN	85,129,148	USD	4,174,000	Citibank N.A.		04/14/21		(15,391	)
MXN	63,857,058	USD	3,131,000	Citibank N.A.		04/14/21		(11,545	)
MXN	63,857,058	USD	3,131,000	Citibank N.A.		04/14/21		(11,545	)
MXN	42,498,319	USD	2,085,500	Citibank N.A.		04/14/21		(9,432	)
MXN	42,631,201	USD	2,085,500	Deutsche Bank AG		04/14/21		(2,940	)
RUB	310,044,720	USD	4,174,000	Bank of America N.A.		04/14/21		(80,993	)
USD	2,714,000	MXN	56,194,727	Citibank N.A.		04/14/21		(31,146	)
USD	3,131,000	MXN	64,146,363	Morgan Stanley & Co. International PLC		04/14/21		(2,588	)
USD	3,131,000	MXN	64,146,363	Morgan Stanley & Co. International PLC		04/14/21		(2,588	)
USD	2,085,500	MXN	43,702,614	Morgan Stanley & Co. International PLC		04/14/21		(49,399	)
USD	3,154,000	MXN	65,498,468	Morgan Stanley & Co. International PLC		04/14/21		(45,639	)
USD	3,132,000	RUB	238,877,640	BNP Paribas S.A.		04/14/21		(21,506	)
USD	18,400,272	ZAR	274,135,036	BNP Paribas S.A.		04/14/21		(137,051	)
USD	5,232,000	ZAR	78,027,432	BNP Paribas S.A.		04/14/21		(44,304	)
USD	2,070,000	ZAR	30,832,973	Citibank N.A.		04/14/21		(14,961	)
USD	4,180,000	ZAR	62,261,355	Citibank N.A.		04/14/21		(30,184	)
USD	4,205,000	ZAR	63,074,521	Deutsche Bank AG		04/14/21		(60,171	)
USD	2,103,000	ZAR	31,413,117	Deutsche Bank AG		04/14/21		(21,191	)
USD	2,093,000	ZAR	31,413,621	UBS AG		04/14/21		(31,225	)
USD	2,093,000	ZAR	31,413,621	UBS AG		04/14/21		(31,225	)
USD	4,176,000	ZAR	62,267,467	UBS AG		04/14/21		(34,597	)
EUR	2,642,000	USD	3,130,829	Barclays Bank PLC		04/15/21		(31,592	)

80 2 0 2 1   BLACK ROCK   SEMI - ANNUAL  REPORT  TO  SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Forward Foreign Currency Exchange Contracts (continued)

Currency Purchased			Currency Sold		Counterparty	Settlement Date		Unrealized Appreciation (Depreciation)
EUR		2,642,000	USD	3,130,829	Barclays Bank PLC		04/15/21	$	(31,592	)
EUR		3,487,000	USD	4,173,299	HSBC Bank PLC		04/15/21		(82,822	)
EUR		3,487,000	USD	4,173,299	HSBC Bank PLC		04/15/21		(82,822	)
RUB		46,700,484	USD	634,464	JPMorgan Chase Bank N.A.		04/15/21		(18,036	)
RUB		242,238,004	USD	3,291,000	JPMorgan Chase Bank N.A.		04/15/21		(93,554	)
TRY		22,874,283	USD	3,119,660	Morgan Stanley & Co. International PLC		04/15/21		(381,392	)
USD		5,564,328	MXN	115,363,215	Bank of America N.A.		04/15/21		(70,622	)
USD		3,111,000	MXN	65,031,411	HSBC Bank PLC		04/15/21		(65,479	)
USD		3,111,000	MXN	65,031,411	HSBC Bank PLC		04/15/21		(65,479	)
KZT		541,216,684	USD	1,270,760	Citibank N.A.		04/20/21		(6,326	)
USD		446,000	TRY	3,793,676	BNP Paribas S.A.		04/26/21		(4,331	)
USD		446,000	TRY	3,773,160	JPMorgan Chase Bank N.A.		04/26/21		(1,896	)
USD		2,104,000	BRL	11,951,562	Citibank N.A.		05/04/21		(14,929	)
USD		2,083,000	BRL	12,092,294	UBS AG		05/04/21		(60,880	)
RUB		275,637,000	USD	3,654,694	BNP Paribas S.A.		05/19/21		(31,747	)
RUB		125,942,463	USD	1,657,116	Citibank N.A.		05/19/21		(1,740	)
RUB		130,207,900	USD	1,726,781	Credit Suisse International		05/19/21		(15,340	)
RUB		75,013,400	USD	993,489	Credit Suisse International		05/19/21		(7,520	)
RUB		133,066,274	USD	1,750,596	HSBC Bank PLC		05/19/21		(1,585	)
RUB		189,093,800	USD	2,493,062	HSBC Bank PLC		05/19/21		(7,631	)
RUB		305,077,179	USD	4,092,249	Morgan Stanley & Co. International PLC		05/19/21		(82,343	)
RUB		130,691,527	USD	1,749,505	Morgan Stanley & Co. International PLC		05/19/21		(31,708	)
IDR		65,648,180,358	USD	4,514,695	Goldman Sachs International		05/24/21		(13,938	)
USD		6,408,275	MXN	133,354,835	Barclays Bank PLC		05/26/21		(75,730	)
USD		5,066,846	MXN	104,345,615	UBS AG		05/26/21		(6,667	)
USD		5,222,000	INR	387,054,640	JPMorgan Chase Bank N.A.		06/09/21		(22,465	)
EUR		26,510,000	GBP	22,783,092	BNP Paribas S.A.		06/16/21		(276,974	)
EUR		35,010,000	GBP	30,019,150	Citibank N.A.		06/16/21		(270,677	)
EUR		4,666,000	USD	5,555,600	Bank of America N.A.		06/16/21		(74,799	)
EUR		33,280,000	USD	39,522,276	Citibank N.A.		06/16/21		(430,749	)
EUR		34,900,000	USD	41,597,233	Citibank N.A.		06/16/21		(602,813	)
EUR		800,000	USD	954,330	Deutsche Bank AG		06/16/21		(14,630	)
EUR		35,535,000	USD	42,394,232	JPMorgan Chase Bank N.A.		06/16/21		(653,925	)
EUR		40,210,000	USD	48,130,284	JPMorgan Chase Bank N.A.		06/16/21		(898,605	)
JPY		1,007,559,907	USD	9,240,000	JPMorgan Chase Bank N.A.		06/16/21		(133,701	)
USD		21,260,150	EUR	18,100,000	HSBC Bank PLC		06/16/21		(567	)
USD	��	557,192	SGD	750,000	Goldman Sachs International		06/16/21		(150	)
USD		4,205,000	IDR	62,023,750,000	Morgan Stanley & Co. International PLC		07/01/21		(36,287	)
									(6,244,267	)
								$	8,338,468

Exchange-Traded Options Purchased

Description	Number of Contracts		Expiration Date			Exercise Price			Notional Amount (000)		Value
Call
Advanced Micro Devices, Inc.		175		04/01/21	USD		84.50	USD		1,374	$	438
Advanced Micro Devices, Inc.		160		04/16/21	USD		84.00	USD		1,256		9,520
Sabre Corp.		100		04/16/21	USD		18.00	USD		148		800
Walt Disney Co.		115		04/16/21	USD		200.00	USD		2,122		9,775
Western Digital Corp.		125		04/16/21	USD		85.00	USD		834		1,938
Western Digital Corp.		240		04/16/21	USD		70.00	USD		1,602		39,840
Invesco QQQ Trust, Series 1 ETF		2,190		04/30/21	USD		330.00	USD		69,889		683,280
Amazon.com, Inc.		109		05/21/21	USD		3,300.00	USD		33,725		600,917
Invesco QQQ Trust, Series 1 ETF		1,093		05/21/21	USD		330.00	USD		34,881		592,406
U.S. Treasury Long-Term Bonds Futures		107		05/21/21	USD		157.00	USD		16,568		128,734

MASTER   PORTFOLIO   SCHEDULE   OF   INVESTMENTS 81

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Exchange-Traded Options Purchased (continued)

Description	Number of Contracts		Expiration Date			Exercise Price			Notional Amount (000)		Value
Western Digital Corp.		125		05/21/21	USD		95.00	USD		834	$	5,875
Caesars Entertainment, Inc.		1,160		06/18/21	USD		70.00	USD		10,144		2,375,100
												4,448,623
Put
iShares iBoxx High Yield Corporate Bond ETF		200		04/01/21	USD		85.00	USD		1,744		1,400
iShares iBoxx High Yield Corporate Bond ETF		400		04/01/21	USD		85.50	USD		3,487		1,200
U.S. Treasury 10-Year Notes Futures		997		04/02/21	USD		131.00	USD		130,654		280,406
Industrial Select Sector SPDR Fund		100		04/16/21	USD		90.00	USD		985		7,550
Invesco QQQ Trust, Series 1 ETF		1,636		04/16/21	USD		305.00	USD		52,210		320,656
iShares iBoxx High Yield Corporate Bond ETF		200		04/16/21	USD		86.00	USD		1,744		5,100
iShares iBoxx High Yield Corporate Bond ETF		250		04/16/21	USD		85.50	USD		2,179		4,500
iShares Russell 2000 ETF		200		04/16/21	USD		205.00	USD		4,419		29,400
NRG Energy, Inc.		75		04/16/21	USD		30.00	USD		283		563
Pitney Bowes, Inc.		252		04/16/21	USD		7.00	USD		208		1,890
SPDR Bloomberg Barclays High Yield Bond ETF		250		04/16/21	USD		106.00	USD		2,720		4,375
SPDR Bloomberg Barclays High Yield Bond ETF		400		04/16/21	USD		105.00	USD		4,352		7,000
U.S. Treasury 10-Year Notes Futures		15		04/23/21	USD		131.50	USD		1,966		14,297
Euro Dollar (3 Year) Mid-Curve		24,355		06/11/21	USD		99.25	USD		5,994,374		49,623,313
Pitney Bowes, Inc.		121		07/16/21	USD		7.00	USD		100		8,168
Euro Dollar (1 Year) Mid-Curve		73,003		09/10/21	USD		99.75	USD		18,183,222		26,463,588
Euro Dollar (2 Year) Mid-Curve		46,948		09/10/21	USD		99.38	USD		11,616,696		51,936,225
Euro Dollar (1 Year) Mid-Curve		2,182		12/10/21	USD		99.50	USD		542,800		763,700
Euro Dollar (1 Year) Mid-Curve		21,131		12/10/21	USD		99.38	USD		5,256,600		5,282,750
												134,756,081
											$	139,204,704

OTC Barrier Options Purchased

Description

Type of Option

Counterparty

Number of Contracts

Expiration Date

Exercise Price

Barrier Price/Range

Notional Amount (000)

Value

Call

EUR Currency

One-Touch

BNP Paribas S.A.

—

06/28/21

USD

1.25

USD

1.25

EUR

12,870

$

405,676

Put

USD Currency

Down-and-Out

Deutsche Bank AG

—

04/20/21

BRL

5.48

BRL

5.24

USD

12,512

30,534

USD Currency

Down-and-Out

Bank of America N.A.

—

04/21/21

RUB

73.75

RUB

71.60

USD

16,684

21,590

USD Currency

Down-and-Out

Goldman Sachs International

—

04/21/21

MXN

20.10

MXN

19.45

USD

10,428

23,186

USD Currency

Down-and-Out

BNP Paribas S.A.

—

04/29/21

RUB

75.00

RUB

72.60

USD

7,350

18,594

EUR Currency

One-Touch

Bank of America N.A.

—

05/06/21

USD

1.16

USD

1.16

EUR

10,243

2,037,619

EUR Currency

One-Touch

BNP Paribas S.A.

—

05/28/21

PLN

4.25

PLN

4.25

EUR

3,730

9,757

EUR Currency

One-Touch

BNP Paribas S.A.

—

05/28/21

HUF

340.00

HUF

340.00

EUR

4,000

32,591

2,173,871

$

2,579,547

OTC Options Purchased

Description	Counterparty	Number of Contracts		Expiration Date			Exercise Price			Notional Amount (000)		Value
Call
USD Currency	Citibank N.A.		—		04/08/21	ZAR		15.60	USD		8,318	$	5,205
USD Currency	JPMorgan Chase Bank N.A.		—		04/08/21	ZAR		15.70	USD		7,278		3,405
USD Currency	Citibank N.A.		—		04/15/21	JPY		110.00	USD		42,470		383,109
USD Currency	Morgan Stanley & Co. International PLC		—		04/15/21	BRL		5.55	USD		3,086		72,626
USD Currency	JPMorgan Chase Bank N.A.		—		04/29/21	CLP		760.00	USD		10,441		24,760
USD Currency	Morgan Stanley & Co. International PLC		—		04/29/21	CLP		730.00	USD		20,882		197,729
USD Currency	Morgan Stanley & Co. International PLC		—		05/06/21	MXN		22.00	USD		6,238		21,519

82 2 0 2 1   BLACK ROCK   SEMI -ANNUAL  REPORT  TO  SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

OTC Options Purchased (continued)

Description	Counterparty	Number of Contracts		Expiration Date			Exercise Price			Notional Amount (000)		Value
EUR Currency	Bank of America N.A.		—		06/09/21	USD		1.23	EUR		174,930	$	177,926
EUR Currency	BNP Paribas S.A.		—		06/18/21	USD		1.23	EUR		175,800		232,276
USD Currency	Citibank N.A.		—		08/10/21	JPY		110.00	USD		57,760		1,077,691
USD Currency	Bank of America N.A.		—		01/12/22	JPY		111.00	USD		74,420		1,544,911
													3,741,157
Put
EUR Currency	Citibank N.A.		—		04/07/21	USD		1.19	EUR		23,258		299,362
EUR Currency	JPMorgan Chase Bank N.A.		—		04/07/21	USD		1.19	EUR		11,699		150,582
EUR Currency	JPMorgan Chase Bank N.A.		—		04/07/21	JPY		128.50	EUR		14,018		10,168
EUR Currency	Bank of America N.A.		—		04/08/21	USD		1.17	EUR		47,255		122,182
USD Currency	Deutsche Bank AG		—		04/08/21	MXN		20.60	USD		14,556		186,041
EUR Currency	Citibank N.A.		—		04/15/21	USD		1.19	EUR		13,966		189,839
EUR Currency	BNP Paribas S.A.		—		04/16/21	USD		1.17	EUR		41,140		172,910
USD Currency	Citibank N.A.		—		04/22/21	TRY		7.50	USD		4,166		8,544
USD Currency	Deutsche Bank AG		—		04/23/21	MXN		19.60	USD		14,780		25,476
USD Currency	Citibank N.A.		—		04/29/21	ZAR		14.80	USD		14,618		255,377
EUR Currency	Morgan Stanley & Co. International PLC		—		05/06/21	USD		1.18	EUR		149,090		1,843,210
EUR Currency	Bank of America N.A.		—		05/14/21	USD		1.18	EUR		111,200		1,459,370
USD Currency	Citibank N.A.		—		05/14/21	RUB		73.00	USD		16,664		86,745
EUR Currency	Goldman Sachs International		—		06/03/21	GBP		0.85	EUR		173,340		1,935,911
EUR Currency	Citibank N.A.		—		06/11/21	GBP		0.85	EUR		175,610		2,090,876
USD Currency	Deutsche Bank AG		—		06/17/21	MXN		20.00	USD		6,261		89,908
USD Currency	Bank of America N.A.		—		07/12/21	JPY		99.00	USD		74,420		28,566
													8,955,067
												$	12,696,224

OTC Credit Default Swaptions Purchased

Notional Amount (000

)

Paid by the Fund

Received by the Fund

Expiration Date

Exercise Price

Description

Rate

Frequency

Rate

Frequency

Counterparty

Value

Put

Bought Protection on 5-Year Credit Default Swap, 12/20/25

5.00%

Quarterly

CDX.NA.HY.35.V1

Quarterly

Bank of America N.A.

04/21/21

105.00

USD

2,000

$

1,371

Bought Protection on 5-Year Credit Default Swap, 12/20/25

5.00%

Quarterly

CDX.NA.HY.35.V1

Quarterly

Bank of America N.A.

04/21/21

107.00

USD

2,500

4,126

$

5,497

OTC Interest Rate Swaptions Purchased

Notional Amount (000)

Paid by the Fund

Received by the Fund

Expiration Date

Exercise Rate

Description

Rate

Frequency

Rate

Frequency

Counterparty

Value

Put

30-Year Interest Rate Swap, 04/17/51

2.17%

Semi-Annual

3-month LIBOR, 0.19%

Quarterly

Citibank N.A.

04/15/21

2.17%

USD    96,799

$

1,814,073

10-Year Interest Rate Swap, 05/12/31

1.85%

Semi-Annual

3-month LIBOR, 0.19%

Quarterly

Citibank N.A.

05/10/21

1.85%

USD  483,993

3,918,332

$

5,732,405

Exchange-Traded Options Written

Description	Number of Contracts		Expiration Date			Exercise Price			Notional Amount (000)		Value
Call
Advanced Micro Devices, Inc.		175		04/01/21	USD		90.00	USD		1,374	$	(175	)
Advanced Micro Devices, Inc.		160		04/16/21	USD		90.00	USD		1,256		(3,040	)

MASTER  PORTFOLIO   SCHEDULE   OF   INVESTMENTS 83

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Exchange-Traded Options Written (continued)

Description	Number of Contracts		Expiration Date			Exercise Price			Notional Amount (000)		Value
UWM Holdings Corp.		1,580		04/16/21	USD		12.50	USD		1,253	$	(7,900	)
Walt Disney Co.		115		04/16/21	USD		210.00	USD		2,122		(3,910	)
Western Digital Corp.		240		04/16/21	USD		76.00	USD		1,602		(14,760	)
Amazon.com, Inc.		164		05/21/21	USD		3,500.00	USD		50,743		(332,920	)
Invesco QQQ Trust, Series 1 ETF		1,092		05/21/21	USD		340.00	USD		34,849		(274,092	)
												(636,797	)
Put
iShares iBoxx High Yield Corporate Bond ETF		600		04/01/21	USD		82.00	USD		5,231		(1,200	)
Invesco QQQ Trust, Series 1 ETF		1,636		04/16/21	USD		295.00	USD		52,210		(150,512	)
iShares iBoxx High Yield Corporate Bond ETF		450		04/16/21	USD		83.00	USD		3,923		(3,600	)
iShares Russell 2000 ETF		200		04/16/21	USD		190.00	USD		4,419		(6,800	)
SPDR Bloomberg Barclays High Yield Bond ETF		400		04/16/21	USD		100.00	USD		4,352		(10,000	)
Amazon.com, Inc.		109		05/21/21	USD		2,500.00	USD		33,726		(120,772	)
U.S. Treasury Long-Term Bonds Futures		272		05/21/21	USD		153.00	USD		42,118		(454,750	)
Euro Dollar (3 Year) Mid-Curve		24,355		06/11/21	USD		98.88	USD		5,994,374		(28,464,906	)
iShares Russell 2000 ETF		823		06/30/21	USD		175.00	USD		18,183		(160,897	)
Euro Dollar (1 Year) Mid-Curve		8,634		09/10/21	USD		99.50	USD		2,150,514		(1,133,213	)
Euro Dollar (2 Year) Mid-Curve		21,046		09/10/21	USD		99.00	USD		5,207,570		(10,917,613	)
Euro Dollar (2 Year) Mid-Curve		25,902		09/10/21	USD		99.13	USD		6,409,126		(17,645,737	)
Euro Dollar (3 Year) Mid-Curve		25,313		09/10/21	USD		98.63	USD		6,219,404		(28,793,537	)
												(87,863,537	)
											$	(88,500,334	)

OTC Options Written

Description	Counterparty	Number of Contracts		Expiration Date		Exercise Price					Notional Amount (000)		Value
Call
EUR Currency	JPMorgan Chase Bank N.A.		—		04/07/21		JPY		130.00	EUR		8,762	$	(25,910	)
USD Currency	JPMorgan Chase Bank N.A.		—		04/08/21		ZAR		16.30	USD		7,278		(721	)
USD Currency	Citibank N.A.		—		04/15/21		JPY		111.50	USD		42,470		(103,994	)
USD Currency	JPMorgan Chase Bank N.A.		—		04/15/21		BRL		5.55	USD		3,086		(72,626	)
USD Currency	Citibank N.A.		—		04/22/21		TRY		7.50	USD		1,782		(195,835	)
USD Currency	Citibank N.A.		—		04/22/21		TRY		7.75	USD		2,083		(171,621	)
USD Currency	Morgan Stanley & Co. International PLC		—		04/29/21		CLP		760.00	USD		20,882		(49,519	)
USD Currency	Bank of America N.A.		—		04/30/21		ZAR		15.70	USD		12,530		(60,303	)
USD Currency	JPMorgan Chase Bank N.A.		—		05/03/21		MXN		21.00	USD		12,462		(123,739	)
USD Currency	Deutsche Bank AG		—		05/06/21		MXN		22.00	USD		6,238		(21,519	)
USD Currency	Morgan Stanley & Co. International PLC		—		05/13/21		BRL	��	5.75	USD		2,572		(47,390	)
USD Currency	Bank of America N.A.		—		07/12/21		JPY		109.00	USD		74,420		(1,687,754	)
														(2,560,931	)
Put
USD Currency	Citibank N.A.		—		04/02/21		RUB		73.00	USD		8,286		(24	)
EUR Currency	Goldman Sachs International		—		04/07/21		USD		1.19	EUR		11,750		(151,239	)
EUR Currency	NatWest Markets PLC		—		04/07/21		USD		1.19	EUR		23,207		(298,706	)
USD Currency	Citibank N.A.		—		04/08/21		ZAR		15.00	USD		8,318		(154,638	)
USD Currency	Deutsche Bank AG		—		04/15/21		MXN		20.00	USD		6,261		(21,616	)
USD Currency	Citibank N.A.		—		04/22/21		TRY		6.85	USD		1,782		(762	)
USD Currency	Deutsche Bank AG		—		04/28/21		MXN		20.00	USD		12,550		(81,426	)
USD Currency	Citibank N.A.		—		04/29/21		ZAR		14.35	USD		15,661		(87,973	)
EUR Currency	Bank of America N.A.		—		05/06/21		USD		1.16	EUR		223,635		(587,821	)
EUR Currency	Bank of America N.A.		—		05/14/21		USD		1.16	EUR		111,200		(490,794	)
EUR Currency	UBS AG		—		05/14/21		USD		1.16	EUR		54,772		(239,051	)
USD Currency	Citibank N.A.		—		05/14/21		RUB		71.00	USD		12,472		(20,317	)
EUR Currency	Citibank N.A.		—		06/11/21		GBP		0.83	EUR		175,610		(511,125	)

84 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

OTC Options Written (continued)

Description	Counterparty	Number of Contracts		Expiration Date		Exercise Price			Notional Amount (000)		Value
USD Currency	Citibank N.A.		—		08/10/21		JPY	97.00	USD	57,760	$	(26,538	)
USD Currency	Bank of America N.A.		—		01/12/22		JPY	97.00	USD	74,420		(176,125	)
												(2,848,155	)
											$	(5,409,086	)

OTC Credit Default Swaptions Written

Notional Amount (000)(b)

Paid by the Fund

Received by the Fund

Expiration Date

Credit Rating(a)

Exercise Price

Description

Rate

Frequency

Rate

Frequency

Counterparty

Value

Put

Sold Protection on 5-Year Credit Default Swap, 12/20/25

CDX.NA.HY.35.V1

Quarterly

5.00%

Quarterly

Bank of America N.A.

04/21/21

N/R

103.00

USD

2,500

$

(1,060

)

^(a)  Using the rating of the issuer or the underlying securities of the index, as applicable, provided by S&P Global Ratings.

^(b)  The maximum potential amount the Master Portfolio may pay should a negative credit event take place as defined under the terms of agreement.

OTC Interest Rate Swaptions Written

Notional Amount (000)

Paid by the Fund

Received by the Fund

Expiration Date

Exercise Rate

Description

Rate

Frequency

Rate

Frequency

Counterparty

Value

Call

10-Year Interest Rate Swap, 02/18/33

1.84%

Semi-Annual

3-month LIBOR, 0.19%

Quarterly

Deutsche Bank AG

02/16/23

1.84%

USD

27,277

$

(609,433

)

10-Year Interest Rate Swap, 02/25/33

1.93%

Semi-Annual

3-month LIBOR, 0.19%

Quarterly

Bank of America N.A.

02/23/23

1.93%

USD

27,273

(687,675

)

(1,297,108

)

Put

30-Year Interest Rate Swap, 04/17/51

3-month LIBOR, 0.19%

Quarterly

2.47%

Semi-Annual

Citibank N.A.

04/15/21

2.47%

USD

145,198

$

(129,681

)

10-Year Interest Rate Swap, 05/12/31

3-month LIBOR, 0.19%

Quarterly

2.15%

Semi-Annual

Citibank N.A.

05/10/21

2.15%

USD

643,711

(1,147,473

)

5-Year Interest Rate Swap, 05/19/26

3-month LIBOR, 0.19%

Quarterly

0.85%

Semi-Annual

Bank of America N.A.

05/17/21

0.85%

USD

197,042

(2,567,807

)

MASTER  PORTFOLIO   SCHEDULE   OF   INVESTMENTS 85

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

OTC Interest Rate Swaptions Written (continued)

Notional Amount (000)

Paid by the Fund

Received by the Fund

Expiration

Exercise

Description

Rate

Frequency

Rate

Frequency

Counterparty

Date

Rate

Value

10-Year Interest Rate Swap, 02/18/33

3-month LIBOR, 0.19%

Quarterly

1.84%

Semi-Annual

Deutsche Bank AG

02/16/23

1.84

%

USD

27,277

$

(1,626,922

)

10-Year Interest Rate Swap, 02/25/33

3-month LIBOR, 0.19%

Quarterly

1.93%

Semi-Annual

Bank of America N.A.

02/23/23

1.93

%

USD

27,273

(1,504,057

)

(6,975,940

)

$

(8,273,048

)

Centrally Cleared Credit Default Swaps — Buy Protection

Reference Obligation/Index	Financing Rate Paid by the Fund			Payment Frequency		Termination Date			Notional Amount (000)	Value			Upfront Premium Paid (Received)			Unrealized Appreciation (Depreciation)
CDX.NA.HY.33.V1		5.00	%		Quarterly		12/20/24	USD	35,459	$	(3,385,360	)	$	(2,460,876	)	$	(924,484	)

Centrally Cleared Inflation Swaps

											Upfront Premium Paid (Received)
							Notional Amount								Unrealized Appreciation (Depreciation	)
Paid by the Fund		Received by the Fund		Termination
Reference	Frequency	Rate	Frequency	Date			(000)	Value
UK RPI All Items Monthly	At Termination	2.52%	At Termination		04/06/26	USD	55,184	$	(1,214	)		$	—	$	(1,214	)
UK RPI All Items Monthly	At Termination	3.42%	At Termination		11/15/30	GBP	13,500		(663,128	)			—		(663,128	)
UK RPI All Items Monthly	At Termination	2.32%	At Termination		01/25/31	USD	91,400		(1,861,039	)			—		(1,861,039	)
UK RPI All Items Monthly	At Termination	2.34%	At Termination		01/25/31	USD	91,400		(1,740,118	)			—		(1,740,118	)
UK RPI All Items Monthly	At Termination	2.32%	At Termination		02/25/31	USD	9,084		(173,698	)			—		(173,698	)
UK RPI All Items Monthly	At Termination	2.35%	At Termination		03/05/31	USD	2,650		(40,862	)			—		(40,862	)
UK RPI All Items Monthly	At Termination	2.35%	At Termination		03/05/31	USD	2,650		(39,741	)			—		(39,741	)
UK RPI All Items Monthly	At Termination	2.36%	At Termination		03/05/31	USD	5,299		(77,521	)			—		(77,521	)
UK RPI All Items Monthly	At Termination	2.35%	At Termination		03/11/31	USD	3,200		(50,453	)			—		(50,453	)
UK RPI All Items Monthly	At Termination	3.33%	At Termination		11/15/40	GBP	7,120		(807,906	)			—		(807,906	)
UK RPI All Items Monthly	At Termination	3.38%	At Termination		12/15/40	GBP	6,820		(628,544	)			—		(628,544	)
UK RPI All Items Monthly	At Termination	3.38%	At Termination		12/15/40	GBP	14,500		(1,330,177	)			—		(1,330,177	)
UK RPI All Items Monthly	At Termination	3.35%	At Termination		02/15/41	GBP	5,000		(565,675	)			—		(565,675	)
UK RPI All Items Monthly	At Termination	3.58%	At Termination		03/15/41	GBP	2,474		(25,890	)			3,367		(29,257	)
UK RPI All Items Monthly	At Termination	3.58%	At Termination		03/15/41	GBP	805		(7,538	)			—		(7,538	)
UK RPI All Items Monthly	At Termination	3.58%	At Termination		03/15/41	GBP	1,610		(13,306	)			—		(13,306	)
								$	(8,026,810	)		$	3,367	$	(8,030,177	)

Centrally Cleared Interest Rate Swaps

Upfront

Notional

Premium

Unrealized

Paid by the Fund

Received by the Fund

Effective

Termination

Amount

Paid

Appreciation

Rate

Frequency

Rate

Frequency

Date

Date

(000

)

Value

(Received)

(Depreciation

)

28-day MXIBTIIE, 4.29%

Monthly

4.29%

Monthly

N/A

01/13/23

MXN

1,081,740

$ (646,502

)

$  754

$

(647,256

)

28-day MXIBTIIE, 4.29%

Monthly

4.18%

Monthly

N/A

02/16/23

MXN

525,194

(401,901

)

74

(401,975

)

28-day MXIBTIIE, 4.29%

Monthly

5.22%

Monthly

N/A

03/29/23

MXN

589,522

75,404

—

75,404

86 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Centrally Cleared Interest Rate Swaps (continued)

											Upfront
							Notional				Premium			Unrealized
Paid by the Fund		Received by the Fund		Effective	Termination		Amount				Paid			Appreciation
Rate	Frequency	Rate	Frequency	Date	Date		(000)		Value		(Received)			(Depreciation)
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	0.78%	Semi-Annual	08/12/22(a)	08/12/23	CAD	50,765	$	(95,355	)	$     —		$	(95,355	)
1-day CORRA, 0.14%	Semi-Annual	0.49%	Semi-Annual	08/16/22(a)	08/16/23	CAD	50,765		(118,385	)	—			(118,385	)
1-day CORRA, 0.14%	Semi-Annual	0.49%	Semi-Annual	08/25/22(a)	08/25/23	CAD	11,000		(27,653	)	—			(27,653	)
1-day CORRA, 0.14%	At Termination	0.48%	At Termination	10/07/22(a)	10/07/23	CAD	260,445		(903,369	)	—			(903,369	)
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	0.76%	Semi-Annual	10/24/22(a)	10/24/23	CAD	130,000		(427,119	)	—			(427,119	)
1-day CORRA, 0.14%	Semi-Annual	0.55%	Semi-Annual	N/A	11/10/23	CAD	130,222		(448,899	)	—			(448,899	)
1-day CORRA, 0.14%	Semi-Annual	0.52%	Semi-Annual	01/10/23(a)	01/10/24	CAD	75,550		(349,557	)	—			(349,557	)
1-day CORRA, 0.14%	Semi-Annual	0.60%	Semi-Annual	01/13/23(a)	01/13/24	CAD	110,000		(449,544	)	—			(449,544	)
1-day CORRA, 0.14%	Semi-Annual	0.54%	Semi-Annual	01/23/23(a)	01/23/24	CAD	314,277		(1,474,127	)	—			(1,474,127	)
28-day MXIBTIIE, 4.29%	Monthly	4.68%	Monthly	N/A	02/27/24	MXN	750,132		(793,870	)	(392	)		(793,478	)
0.75%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	03/01/23(a)	03/01/24	USD	147,705		226,010		—			226,010
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	1.37%	Semi-Annual	03/01/23(a)	03/01/24	CAD	188,380		(129,238	)	—			(129,238	)
0.70%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	03/02/23(a)	03/02/24	USD	73,852		154,255		—			154,255
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	1.36%	Semi-Annual	03/02/23(a)	03/02/24	CAD	94,190		(78,196	)	—			(78,196	)
28-day MXIBTIIE, 4.29%	Monthly	5.47%	Monthly	N/A	03/21/24	MXN	189,156		(3,322	)	—			(3,322	)
28-day MXIBTIIE, 4.29%	Monthly	5.50%	Monthly	N/A	03/21/24	MXN	189,377		4,514		—			4,514
0.51%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	N/A	04/06/24	USD	164,023		11,739		—			11,739
0.63%	At Termination	1-day SONIA, 0.05%	At Termination	03/01/24(a)	03/01/25	GBP	222,360		225,966		—			225,966
0.64%	At Termination	1-day SONIA, 0.05%	At Termination	03/01/24(a)	03/01/25	GBP	222,360		216,864		—			216,864
0.61%	At Termination	1-day SONIA, 0.05%	At Termination	03/11/24(a)	03/11/25	GBP	312,110		453,350		—			453,350
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	0.75%	Semi-Annual	N/A	05/26/25	CAD	17,415		(269,562	)	(47	)		(269,515	)
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	0.82%	Semi-Annual	N/A	06/03/25	CAD	5,855		(78,035	)	(25	)		(78,010	)
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	0.82%	Semi-Annual	N/A	06/03/25	CAD	5,855		(79,068	)	(49	)		(79,019	)

MASTER  PORTFOLIO   SCHEDULE   OF  INVESTMENTS 87

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Centrally Cleared Interest Rate Swaps (continued)

											Upfront
							Notional				Premium					Unrealized
Paid by the Fund		Received by the Fund		Effective	Termination		Amount				Paid					Appreciation
Rate	Frequency	Rate	Frequency	Date	Date		(000)		Value		(Received)					(Depreciation)
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	0.74%	Semi-Annual	N/A	09/18/25	CAD	13,320	$	(272,755	)		$	(173	)	$	(272,582	)
3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	0.75%	Semi-Annual	N/A	09/18/25	CAD	13,000		(263,226	)			(174	)		(263,052	)
0.78%	Semi-Annual	3-month Canadian Bankers Acceptances, 0.44%	Semi-Annual	N/A	11/02/25	CAD	44,905		885,585				270			885,315
2.91%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	N/A	08/23/26	USD	3,692		(359,932	)			(46	)		(359,886	)
2.93%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	N/A	08/24/28	USD	8,170		(865,056	)			128			(865,184	)
3.16%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	N/A	10/03/28	USD	4,519		(609,933	)			71			(610,004	)
0.68%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	N/A	09/23/30	USD	19,409		1,815,050				—			1,815,050
3-month LIBOR, 0.19%	Quarterly	0.67%	Semi-Annual	N/A	09/23/30	USD	19,409		(1,836,077	)			—			(1,836,077	)
3-month LIBOR, 0.19%	Quarterly	1.25%	Semi-Annual	N/A	02/16/31	USD	47,011		(2,177,425	)			—			(2,177,425	)
3-month LIBOR, 0.19%	Quarterly	1.46%	Semi-Annual	N/A	02/24/31	USD	38,719		(1,024,555	)			—			(1,024,555	)
1-day SONIA, 0.05%	Semi-Annual	0.70%	Semi-Annual	N/A	03/25/31	GBP	6,558		(95,665	)			(159	)		(95,506	)
3-month LIBOR, 0.19%	Quarterly	2.22%	Semi-Annual	06/30/21(a)	02/15/47	USD	48,158		106,698				—			106,698
1.50%	Semi-Annual	3-month LIBOR, 0.19%	Quarterly	N/A	03/08/51	USD	100,067		15,754,437				—			15,754,437
3-month LIBOR, 0.19%	Quarterly	1.70%	Semi-Annual	N/A	03/08/51	USD	50,034		(5,560,418	)			—			(5,560,418	)
3-month LIBOR, 0.19%	Quarterly	1.77%	Semi-Annual	N/A	03/08/51	USD	50,034		(4,749,535	)			—			(4,749,535	)
0.85%	Semi-Annual	1-day SONIA, 0.05%	Semi-Annual	N/A	03/25/51	GBP	2,388		113,087				71			113,016
								$	(4,545,320)			$	303		$	(4,545,623	)

^(a)  Forward swap.

OTC Credit Default Swaps — Buy Protection

Reference Obligation/Index	Financing Rate Paid by the Fund			Payment Frequency	Counterparty	Termination Date				Notional Amount (000)		Value			Upfront Premiun Paid (Received)			Unrealized Appreciation (Depreciation)
DISH DBS Corp.		5.00	%	Quarterly	Goldman Sachs International		12/20/23	��	USD		2,168		$ (130,099	)		$ 60,826			$ (190,925	)
KB Home		5.00		Quarterly	JPMorgan Chase Bank N.A.		12/20/23		USD		2,138		(223,118	)		(97,775	)		(125,343	)
Realogy Group LLC		5.00		Quarterly	JPMorgan Chase Bank N.A.		12/20/23		USD		1,070		(73,920	)		(5,715	)		(68,205	)
RR Donnelley & Sons Co.		5.00		Quarterly	JPMorgan Chase Bank N.A.		12/20/23		USD		1,070		(38,033	)		29,563			(67,596	)
Beazer Homes USA, Inc.		5.00		Quarterly	Barclays Bank PLC		06/20/24		USD		1,199		(110,367	)		(51,615	)		(58,752	)
Beazer Homes USA, Inc.		5.00		Quarterly	BNP Paribas S.A.		06/20/24		USD		1,000		(92,049	)		(38,011	)		(54,038	)
Beazer Homes USA, Inc.		5.00		Quarterly	BNP Paribas S.A.		06/20/24		USD		1,103		(101,530	)		(45,243	)		(56,287	)
Tenet Healthcare Corp.		5.00		Quarterly	Barclays Bank PLC		06/20/24		USD		1,000		(78,978	)		(7,586	)		(71,392	)
Tenet Healthcare Corp.		5.00		Quarterly	Goldman Sachs International		06/20/24		USD		1,175		(95,833	)		(27,343	)		(68,490	)
Tenet Healthcare Corp.		5.00		Quarterly	Goldman Sachs International		06/20/24		USD		1,150		(93,794	)		(26,761	)		(67,033	)
Tenet Healthcare Corp.		5.00		Quarterly	Goldman Sachs International		06/20/24		USD		1,175		(95,833	)		(27,367	)		(68,466	)

88 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT    TO   SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

OTC Credit Default Swaps — Buy Protection (continued)

Reference Obligation/Index	Financing Rate Paid by the Fund			Payment Frequency	Counterparty	Termination Date			Notional Amount (000)		Value			Upfront Premiun Paid (Received)			Unrealized Appreciation (Depreciation)
Tenet Healthcare Corp.		5.00	%	Quarterly	Goldman Sachs International		06/20/24	USD		1,223	$	(96,590	)	$	(11,222	)	$	(85,368	)
Tenet Healthcare Corp.		5.00		Quarterly	JPMorgan Chase Bank N.A.		06/20/24	USD		500		(40,780	)		(4,442	)		(36,338	)
Avis Budget Group, Inc.		5.00		Quarterly	JPMorgan Chase Bank N.A.		12/20/24	USD		750		(78,855	)		47,242			(126,097	)
Avis Budget Group, Inc.		5.00		Quarterly	JPMorgan Chase Bank N.A.		12/20/24	USD		1,680		(173,048	)		104,851			(277,899	)
Boeing Co.		1.00		Quarterly	BNP Paribas S.A.		12/20/24	USD		2,250		(12,991	)		(33,424	)		20,433
Boeing Co.		1.00		Quarterly	Morgan Stanley & Co. International PLC		12/20/24	USD		5,950		(34,353	)		(52,320	)		17,967
Broadcom, Inc.		1.00		Quarterly	JPMorgan Chase Bank N.A.		12/20/24	USD		1,325		(27,740	)		30,254			(57,994	)
Occidental Petroleum Corp.		1.00		Quarterly	Barclays Bank PLC		12/20/24	USD		5,080		280,409			1,983,367			(1,702,958	)
Avis Budget Group, Inc.		5.00		Quarterly	JPMorgan Chase Bank N.A.		06/20/25	USD		2,540		(268,492	)		266,268			(534,760	)
Federative Republic of Brazil		1.00		Quarterly	Barclays Bank PLC		06/20/26	USD		40,344		2,405,503			2,323,263			82,240
Republic of Chile		1.00		Quarterly	Goldman Sachs International		06/20/26	USD		5,147		(108,925	)		(107,084	)		(1,841	)
Republic of Colombia		1.00		Quarterly	Citibank N.A.		06/20/26	USD		51,762		877,708			823,482			54,226
Republic of Indonesia		1.00		Quarterly	JPMorgan Chase Bank N.A.		06/20/26	USD		31,972		(186,027	)		(184,196	)		(1,831	)
Republic of South Africa		1.00		Quarterly	Goldman Sachs International		06/20/26	USD		11,766		762,019			835,537			(73,518	)
Republic of South Africa		1.00		Quarterly	Goldman Sachs International		06/20/26	USD		80,567		5,218,083			5,700,783			(482,700	)
Republic of South Africa		1.00		Quarterly	Goldman Sachs International		06/20/26	USD		6,766		438,225			478,763			(40,538	)
Republic of the Philippines		1.00		Quarterly	Goldman Sachs International		06/20/26	USD		11,217		(316,706	)		(302,622	)		(14,084	)
Russian Federation		1.00		Quarterly	Citibank N.A.		06/20/26	USD		21,421		114,260			93,973			20,287
United Mexican States		1.00		Quarterly	Morgan Stanley & Co. International PLC		06/20/26	USD		45,588		307,610			300,056			7,554
CMBX.NA.9.AAA		0.50		Monthly	Credit Suisse International		09/17/58	USD		4,539		(44,297	)		50,688			(94,985	)
CMBX.NA.9.AAA		0.50		Monthly	Deutsche Bank AG		09/17/58	USD		3,620		(35,320	)		41,001			(76,321	)
CMBX.NA.9.AAA		0.50		Monthly	Morgan Stanley & Co. International PLC		09/17/58	USD		2,530		(24,685	)		28,247			(52,932	)
CMBX.NA.9.AAA		0.50		Monthly	Morgan Stanley & Co. International PLC		09/17/58	USD		3,050		(29,758	)		34,053			(63,811	)
CMBX.NA.9.AAA		0.50		Monthly	Morgan Stanley & Co. International PLC		09/17/58	USD		5,569		(54,346	)		68,235			(122,581	)
CMBX.NA.9.BBB-		3.00		Monthly	Citigroup Global Markets, Inc.		09/17/58	USD		2,080		228,238			69,784			158,454
CMBX.NA.9.BBB-		3.00		Monthly	Morgan Stanley & Co. International PLC		09/17/58	USD		204		22,385			11,206			11,179
CMBX.NA.6.AAA		0.50		Monthly	Deutsche Bank AG		05/11/63	USD		2,155		(9,445	)		392			(9,837	)
CMBX.NA.6.AAA		0.50		Monthly	Deutsche Bank AG		05/11/63	USD		5,237		(22,949	)		(1,598	)		(21,351	)
CMBX.NA.6.BBB-		3.00		Monthly	J.P. Morgan Securities LLC		05/11/63	USD		850		228,909			78,452			150,457
CMBX.NA.14.BBB-		3.00		Monthly	Goldman Sachs International		12/16/72	USD		1,310		62,269			66,742			(4,473	)
											$	8,246,757		$	12,502,704		$	(4,255,947	)

OTC Credit Default Swaps — Sell Protection

Reference Obligation/Index	Financing Rate Received by the Fund			Payment Frequency	Counterparty	Termination Date		Credit Rating(a)		Notional Amount (000)(b)			Value		Upfront Premium Paid (Received)			Unrealized Appreciation (Depreciation)
Broadcom, Inc.		1.00	%	Quarterly	Citibank N.A.		06/20/24	BBB-	USD		14,931		$	313,813		$ (736,703	)	$	1,050,516
T-Mobile USA, Inc.		5.00		Quarterly	Citibank N.A.		12/20/25	BB	USD		2,000			353,859		356,140			(2,281	)
T-Mobile USA, Inc.		5.00		Quarterly	Citibank N.A.		12/20/25	BB	USD		1,000			176,929		177,870			(941	)
T-Mobile USA, Inc.		5.00		Quarterly	Citibank N.A.		12/20/25	BB	USD		1,000			176,929		175,369			1,560
Yum! Brands, Inc.		1.00		Quarterly	BNP Paribas S.A.		12/20/25	BB-	USD		2,000			9,548		(13,575	)		23,123
Yum! Brands, Inc.		1.00		Quarterly	BNP Paribas S.A.		12/20/25	BB-	USD		2,000			9,548		(18,040	)		27,588
Yum! Brands, Inc.		1.00		Quarterly	JPMorgan Chase Bank N.A.		12/20/25	BB-	USD		2,000			9,548		(8,170	)		17,718
Advanced Micro Devices, Inc.		5.00		Quarterly	Goldman Sachs International		06/20/26	BBB-	USD		4,000			883,091		863,056			20,035
AT&T Inc.		1.00		Quarterly	Credit Suisse International		06/20/26	BBB	USD		3,000			46,329		43,885			2,444
HCA, Inc.		5.00		Quarterly	Citibank N.A.		06/20/26	BB-	USD		5,000			968,497		933,721			34,776
NRG Energy, Inc.		5.00		Quarterly	Barclays Bank PLC		06/20/26	BB+	USD		2,000			322,703		297,203			25,500
CMBX.NA.7.AAA		0.50		Monthly	Morgan Stanley & Co. International PLC		01/17/47	AAA	USD		4,964			37,792		(138,769	)		176,561
CMBX.NA.3.AM		0.50		Monthly	Credit Suisse International		12/13/49	N/R	USD		—	(c)		—		(10	)		10

MASTER   PORTFOLIO    SCHEDULE    OF   INVESTMENTS 89

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

OTC Credit Default Swaps — Sell Protection (continued)

Reference Obligation/Index	Financing Rate Received by the Fund		Payment   Frequency	Counterparty	Termination Date	Credit Rating	(a)	Notional Amount (000)(b)				Value			Upfront Premium Paid (Received)			Unrealized Appreciation (Depreciation)
CMBX.NA.3.AM	0.50	%	Monthly	Goldman Sachs International	12/13/49	N/R		USD	—	(c)	$	—		$	(24	)	$	24
CMBX.NA.3.AM	0.50		Monthly	JPMorgan Chase Bank N.A.	12/13/49	N/R		USD	1			—			(50	)		50
CMBX.NA.9.BBB-	3.00		Monthly	Deutsche Bank AG	09/17/58	N/R		USD	906			(99,415	)		(102,908	)		3,493
CMBX.NA.9.BBB-	3.00		Monthly	Goldman Sachs International	09/17/58	N/R		USD	1,310			(143,746	)		(144,913	)		1,167
CMBX.NA.9.BBB-	3.00		Monthly	J.P. Morgan Securities LLC	09/17/58	N/R		USD	438			(48,061	)		(36,699	)		(11,362	)
CMBX.NA.9.BBB-	3.00		Monthly	J.P. Morgan Securities LLC	09/17/58	N/R		USD	800			(87,784	)		(179,077	)		91,293
CMBX.NA.9.BBB-	3.00		Monthly	Morgan Stanley & Co. International PLC	09/17/58	N/R		USD	1,000			(109,730	)		(261,455	)		151,725
CMBX.NA.9.BBB-	3.00		Monthly	Morgan Stanley & Co. International PLC	09/17/58	N/R		USD	1,060			(116,313	)		(50,849	)		(65,464	)
CMBX.NA.9.BBB-	3.00		Monthly	Morgan Stanley & Co. International PLC	09/17/58	N/R		USD	231			(25,347	)		(13,322	)		(12,025	)
CMBX.NA.9.BBB-	3.00		Monthly	Morgan Stanley & Co. International PLC	09/17/58	N/R		USD	1,200			(131,676	)		(1,478	)		(130,198	)
CMBX.NA.10.A	2.00		Monthly	Deutsche Bank AG	11/17/59	A-		USD	3,340			(73,313	)		(137,774	)		64,461
CMBX.NA.10.A	2.00		Monthly	Deutsche Bank AG	11/17/59	A-		USD	1,670			(36,656	)		(70,044	)		33,388
CMBX.NA.10.BBB-	3.00		Monthly	J.P. Morgan Securities LLC	11/17/59	BBB-		USD	60			(7,486	)		(4,897	)		(2,589	)
CMBX.NA.6.BBB-	3.00		Monthly	Credit Suisse International	05/11/63	BB-		USD	850			(228,910	)		(63,531	)		(165,379	)
											$	2,200,149		$	864,956		$	1,335,193

^(a)  Using the rating of the issuer or the underlying securities of the index, as applicable, provided by S&P Global Ratings.

^(b)  The maximum potential amount the Master Portfolio may pay should a negative credit event take place as defined under the terms of agreement.

^(c)  Notional amount is less than USD 500.

OTC Interest Rate Swaps

									Notional Amount (000)					Upfront Premium Paid (Received)			Unrealized Appreciation (Depreciation)
Paid by the Fund			Received by the Fund				Termination Date
Rate	Frequency		Rate	Frequency		Counterparty					Value
3.27%		Semi-Annual	3-month LIBOR, 0.19%		Quarterly	Deutsche Bank AG	05/16/21	USD		9,510	$	(151,718	)		$	—		$	(151,718	)
1.42%		Semi-Annual	1-day CLICP, 18,991.34		Semi-Annual	Bank of America N.A.	04/01/23	CLP		19,436,176		47,321				—			47,321
											$	(104,397	)		$	—		$	(104,397	)

OTC Inflation Rate Swaps

							Notional				Upfront Premium				Unrealized
Paid by the Fund		Received by the Fund			Termination		Amount				Paid				Appreciation
Reference	Frequency	Rate	Frequency	Counterparty	Date		(000)		Value		(Received)				(Depreciation)
U.S. CPI Urban Consumers NAS (CPURNSA)	At Termination	(0.60)%	At Termination	Citibank N.A.	04/15/21	USD	76,393	$	(1,601,478	)		$	—	$	(1,601,478	)
0.27%	At Termination	U.S. CPI Urban Consumers NAS (CPURNSA)	At Termination	Citibank N.A.	04/15/22	USD	76,394		2,770,365				—		2,770,365
								$	1,168,887			$	—	$	1,168,887

90 2 0 2 1   BLACK ROCK  SEMI - ANNUAL  REPORT   TO  SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

OTC Total Return Swaps

							Notional Amount (000)						Upfront Premium Paid (Received)			Unrealized Appreciation (Depreciation)
Paid by the Fund			Received by the Fund			Termination Date
Reference	Frequency		Rate	Frequency	Counterparty					Value
Diamondback Energy, Inc.		At Termination	3-month LIBOR, 0.19%	At Termination	Credit Suisse International	06/09/21		USD	119	$	11,795			$	—		$	11,795
Diamondback Energy, Inc.		At Termination	3-month LIBOR, 0.19%	At Termination	Credit Suisse International	06/09/21		USD	159		23,843				—			23,843
Diamondback Energy, Inc.		At Termination	3-month LIBOR, 0.19%	At Termination	Credit Suisse International	06/09/21		USD	359		48,755				—			48,755
3-month LIBOR, 0.19%		At Termination	Goldman Sachs Systematic Skew U.S. Series 10 Excess Return Strategy	At Termination	Goldman Sachs International	09/09/21		USD	3,119		16,196				—			16,196
ConocoPhillips		At Termination	3-month LIBOR minus 0.30%, 0.19%	At Termination	Credit Suisse International	10/18/21		USD	3,100		(408,263	)			—			(408,263	)
Choice Hotels International, Inc.		At Termination	3-month LIBOR minus 0.20%, 0.19%	At Termination	BNP Paribas S.A.	11/15/21		USD	2,148		38,628				—			38,628
										$	(269,046	)		$	—		$	(269,046	)

Balances Reported in the Statement of Assets and Liabilities for Centrally Cleared Swaps, OTC Swaps and Options Written

	Swaps Premiums Paid		Swap Premiums Received			Unrealized Appreciation		Unrealized Depreciation			Value
Centrally Cleared Swaps	$	4,735	$	(2,461,941	)	$	20,042,618	$	(33,542,902	)	$	—
OTC Swaps		16,374,272		(3,006,612	)		5,205,132		(7,330,442	)		—
Options Written		N/A		N/A			2,972,934		(67,258,595	)		(102,183,528	)

Derivative Financial Instruments Categorized by Risk Exposure

As of period end, the fair values of derivative financial instruments located in the Statement of Assets and Liabilities were as follows:

	Commodity Contracts		Credit Contracts		Equity Contracts		Foreign Currency Exchange Contracts		Interest Rate Contracts		Other Contracts		Total
Assets — Derivative Financial Instruments
Futures contracts
Unrealized appreciation(a)		$  —	$	—	$	15,020	$	—	$	43,964,558	$	—	$	43,979,578
Forward foreign currency exchange contracts
Unrealized appreciation on forward foreign currency exchange contracts		—		—		—		14,582,735		—		—		14,582,735
Options purchased
Investments at value — unaffiliated(b)		—		5,497		4,711,691		15,275,771		140,225,418		—		160,218,377
Swaps — centrally cleared
Unrealized appreciation(a)		—		—		—		—		20,042,618		—		20,042,618
Swaps — OTC
Unrealized appreciation on OTC swaps; Swap premiums paid		—		18,622,501		139,217		—		47,321		2,770,365		21,579,404
		$  —	$	18,627,998	$	4,865,928	$	29,858,506	$	204,279,915	$	2,770,365	$	260,402,712

MASTER  PORTFOLIO   SCHEDULE   OF  INVESTMENTS 91

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

	Commodity Contracts		Credit Contracts		Equity Contracts		Foreign Currency Exchange Contracts		Interest Rate Contracts		Other Contracts		Total
Liabilities — Derivative Financial Instruments
Futures contracts
Unrealized depreciation(a)		$  —	$	—	$	978,931	$	—	$	64,554,135	$	—	$	65,533,066
Forward foreign currency exchange contracts
Unrealized depreciation on forward foreign currency exchange contracts		—		—		—		6,244,267		—		—		6,244,267
Options written
Options written at value		—		1,060		1,090,578		5,409,086		95,682,804		—		102,183,528
Swaps — centrally cleared
Unrealized depreciation(a)		—		924,484		—		—		24,588,241		8,030,177		33,542,902
Swaps — OTC
Unrealized depreciation on OTC swaps;
Swap premiums received		—		8,175,595		408,263		—		151,718		1,601,478		10,337,054
		$  —	$	9,101,139	$	2,477,772	$	11,653,353	$	184,976,898	$	9,631,655	$	217,840,817

^(a)  Net cumulative unrealized appreciation (depreciation) on futures and centrally cleared swaps, if any, are reported in the Schedule of Investments. In the Statement of Assets and Liabilities, only current day’s variation margin is reported in receivables or payables and the net cumulative unrealized appreciation (depreciation) is included in accumulated earnings (loss).

^(b)  Includes options purchased at value as reported in the Schedule of Investments.

For the six months ended March 31, 2021, the effect of derivative financial instruments in the Statement of Operations was as follows:

	Commodity Contracts		Credit Contracts			Equity Contracts			Foreign Currency Exchange Contracts			Interest Rate Contracts			Other Contracts			Total
Net Realized Gain (Loss) from
Futures contracts		$  —	$	—		$	916,755		$	—		$	(214,265,323	)	$	—		$	(213,348,568	)
Forward foreign currency exchange contracts		—		—			—			(51,520,019	)		—			—			(51,520,019	)
Options purchased(a)		—		(26,800	)		3,953,271			(36,339,583	)		17,950,230			—			(14,462,882	)
Options written		—		5,000			10,520,899			20,371,040			(12,252,259	)		—			18,644,680
Swaps		—		(9,023,469	)		(3,504,038	)		—			(17,932,416	)		(5,611,105	)		(36,071,028	)
		$  —	$	(9,045,269	)	$	11,886,887		$	(67,488,562	)	$	(226,499,768	)	$	(5,611,105	)	$	(296,757,817	)
Net Change in Unrealized Appreciation (Depreciation) on
Futures contracts		$  —	$	—		$	(1,010,080	)	$	—		$	(15,759,126	)	$	—		$	(16,769,206	)
Forward foreign currency exchange contracts		—		—			—			5,851,467			—			—			5,851,467
Options purchased		—		(15,233	)		(2,231,696	)		5,582,997			109,336,601			—			112,672,669
Options written		—		2,990			103,819			(2,913,218	)		(64,731,624	)		—			(67,538,033	)
Swaps		—		(5,068,923	)		(1,640,153	)		—			(3,289,979	)		(11,954,344	)		(21,953,399	)
		$  —	$	(5,081,166	)	$	(4,778,110	)	$	8,521,246		$	25,555,872		$	(11,954,344	)	$	12,263,498

^(a)  Options purchased are included in net realized gain (loss) from investments — unaffiliated.

Average Quarterly Balances of Outstanding Derivative Financial Instruments

Futures contracts
Average notional value of contracts — long	$	6,499,542,628
Average notional value of contracts — short	$	4,814,288,038
Forward foreign currency exchange contracts
Average amounts purchased — in USD	$	2,199,846,250
Average amounts sold — in USD	$	1,160,037,519
Options
Average value of option contracts purchased	$	109,678,268
Average value of option contracts written	$	54,562,591
Average notional value of swaption contracts purchased	$	513,342,100
Average notional value of swaption contracts written	$	879,818,852

92 2 0 2 1   BLACK ROCK  SEMI - ANNUAL  REPORT   TO  SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Average Quarterly Balances of Outstanding Derivative Financial Instruments (continued)

Credit default swaps
Average notional value — buy protection	$	416,508,912
Average notional value — sell protection	$	44,105,597
Total return swaps
Average notional amount	$	9,212,969
Interest rate swaps
Average notional value — pays fixed rate	$	3,134,819,563
Average notional value — received fixed rate	$	1,297,184,829
Inflation swaps
Average notional amount — pays	$	687,436,660
Average notional amount — receives	$	341,594,717

For more information about the Master Portfolio’s investment risks regarding derivative financial instruments, refer to the Notes to Financial Statements.

Derivative Financial Instruments – Offsetting as of Period End

The Master Portfolio’s derivative assets and liabilities (by type) were as follows:

	Assets			Liabilities
Derivative Financial Instruments
Futures contracts	$	4,193,678		$	8,172,329
Forward foreign currency exchange contracts		14,582,735			6,244,267
Options		160,218,377(a)			102,183,528
Swaps — centrally cleared		1,552,141			—
Swaps — OTC(b)		21,579,404			10,337,054
Total derivative assets and liabilities in the Statement of Assets and Liabilities	$	202,126,335		$	126,937,178
Derivatives not subject to a Master Netting Agreement or similar agreement (“MNA”)		(144,950,523	)		(96,672,663	)
Total derivative assets and liabilities subject to an MNA	$	57,175,812		$	30,264,515

^(a)  Includes options purchased at value which is included in Investments at value — unaffiliated in the Statement of Assets and Liabilities and reported in the Schedule of Investments.

^(b)  Includes unrealized appreciation (depreciation) on OTC swaps in the Statement of Assets and Liabilities.

The following tables present the Master Portfolio’s derivative assets and liabilities by counterparty net of amounts available for offset under an MNA and net of the related collateral received and pledged by the Master Portfolio:

Counterparty	Derivative Assets Subject to an MNA by Counterparty		Derivatives Available for Offset(a)			Non- Cash Collateral Received(b)			Cash Collateral Received(b)			Net Amount of Derivative Assets(c)(d)
Bank of America N.A.	$	6,648,485	$	(6,648,485	)	$	—		$	—		$	—
Bank of Montreal		155,438		—			—			—			155,438
Bank of New York Mellon		76,014		—			—			—			76,014
Barclays Bank PLC		5,159,363		(2,031,217	)		(2,676,116	)		—			452,030
BNP Paribas S.A.		6,073,799		(816,171	)		—			(1,130,000	)		4,127,628
Citibank N.A.		19,046,760		(6,477,095	)		—			(12,569,665	)		—
Citigroup Global Markets, Inc.		228,238		—			—			(228,238	)		—
Credit Suisse International		201,868		(201,868	)		—			—			—
Deutsche Bank AG		791,661		(791,661	)		—			—			—
Goldman Sachs International		10,002,226		(1,910,099	)		—			(7,990,000	)		102,127
HSBC Bank PLC		2,386,658		(306,385	)		(419,172	)		—			1,661,101
J.P. Morgan Securities LLC		320,202		(234,624	)		—			—			85,578(e)
JPMorgan Chase Bank N.A.		1,882,166		(1,882,166	)		—			—			—
Morgan Stanley & Co. International PLC		3,361,367		(1,694,057	)		—			(1,667,310	)		—
Standard Chartered Bank		228,618		—			—			—			228,618
State Street Bank and Trust Co.		421,441		—			—			—			421,441
UBS AG		191,508		(191,508	)		—			—			—
	$	57,175,812	$	(23,185,336	)	$	(3,095,288	)	$	(23,585,213	)	$	7,309,975

MASTER  PORTFOLIO   SCHEDULE   OF  INVESTMENTS 93

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

Counterparty	Derivative Liabilities Subject to an MNA by Counterparty		Derivatives Available for Offset(a)			Non- Cash Collateral Pledged(f)			Cash Collateral Pledged(f)			Net Amount of Derivative Liabilities(d)(g)
Bank of America N.A.	$	7,989,810	$	(6,648,485	)	$	—		$	—		$	1,341,325
Barclays Bank PLC		2,031,217		(2,031,217	)		—			—			—
BNP Paribas S.A.		816,171		(816,171	)		—			—			—
Citibank N.A.		6,477,095		(6,477,095	)		—			—			—
Credit Suisse International		755,028		(201,868	)		—			(553,160	)		—
Deutsche Bank AG		3,222,416		(791,661	)		(2,430,755	)		—			—
Goldman Sachs International		1,910,099		(1,910,099	)		—			—			—
HSBC Bank PLC		306,385		(306,385	)		—			—			—
J.P. Morgan Securities LLC		234,624		(234,624	)		—			—			—
JPMorgan Chase Bank N.A.		3,810,624		(1,882,166	)		—			(480,000	)		1,448,458
Morgan Stanley & Co. International PLC		1,694,057		(1,694,057	)		—			—			—
NatWest Markets PLC		298,706		—			—			—			298,706
UBS AG		718,283		(191,508	)		—			(460,000	)		66,775
	$	30,264,515	$	(23,185,336	)	$	(2,430,755	)	$	(1,493,160	)	$	3,155,264

^(a)  The amount of derivatives available for offset is limited to the amount of derivative assets and/or liabilities that are subject to an MNA.

^(b)  Excess of collateral received from the individual counterparty is not shown for financial reporting purposes.

^(c)  Net amount represents the net amount receivable from the counterparty in the event of default.

^(d)  Net amount may also include forward foreign currency exchange contracts that are not required to be collateralized.

^(e)  Net amount payable is subject to set-off provision and is netted against net amount receivable under the MSLA.

^(f)  Excess of collateral pledged to the individual counterparty is not shown for financial reporting purposes.

^(g)  Net amount represents the net amount payable due to the counterparty in the event of default. Net amount may be offset further by the options written receivable/payable on the Statement of Assets and Liabilities.

Fair Value Hierarchy as of Period End

Various inputs are used in determining the fair value of financial instruments. For description of the input levels and information about the Master Portfolio’s policy regarding valuation of financial instruments, refer to the Notes to Financial Statements.

The following table summarizes the Master Portfolio’s investments categorized in the fair value hierarchy. The breakdown of the Master Portfolio’s investments into major categories is disclosed in the Schedule of Investments above.

	Level 1		Level 2		Level 3		Total
Assets
Investments
Long-Term Investments
Asset-Backed Securities	$	—	$	2,205,325,286	$	163,666,402	$	2,368,991,688
Common Stocks
Capital Markets		—		11,410,120		—		11,410,120
Diversified Financial Services		33,852,844		—		272,129		34,124,973
Energy Equipment & Services		1,882		—		42,212		44,094
Equity Real Estate Investment Trusts (REITs)		29,137,390		—		—		29,137,390
Health Care Providers & Services		1,114,219		—		—		1,114,219
Hotels, Restaurants & Leisure		25,990,140		—		—		25,990,140
Household Durables		10,731,058		—		—		10,731,058
Internet & Direct Marketing Retail		14,418,413		—		—		14,418,413
IT Services		74,050		—		—		74,050
Media		2,506,567		—		—		2,506,567
Metals & Mining		30,517		—		—		30,517
Oil, Gas & Consumable Fuels		18,544,112		3,706,217		—		22,250,329
Real Estate Management & Development		20,653,692		—		—		20,653,692
Corporate Bonds		—		7,839,499,415		34,874,989		7,874,374,404
Floating Rate Loan Interests		—		253,612,787		105,541,670		359,154,457
Foreign Agency Obligations		—		149,293,427		—		149,293,427
Foreign Government Obligations		—		1,442,158,863		—		1,442,158,863
Municipal Bonds		—		136,601,565		—		136,601,565
Non-Agency Mortgage-Backed Securities		—		1,169,553,425		74,155,154		1,243,708,579
Preferred Securities		—		137,034,564		—		137,034,564

94 2 0 2 1   BLACK ROCK  SEMI - ANNUAL  REPORT   TO  SHAREHOLDERS

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

	Level 1			Level 2			Level 3			Total
Rights	$	—		$	—		$	321,840		$	321,840
U.S. Government Sponsored Agency Securities		—			12,403,094,373			—			12,403,094,373
U.S. Treasury Obligations		—			2,077,537,497			—			2,077,537,497
Warrants
Diversified Financial Services		3,332,720			—			459,035			3,791,755
Oil, Gas & Consumable Fuels		146,891			836,029			—			982,920
Real Estate Management & Development		1,408			—			—			1,408
Short-Term Securities
Money Market Funds		1,842,635,593			—			—			1,842,635,593
Options Purchased
Credit Contracts		—			5,497			—			5,497
Equity Contracts		4,711,691			—			—			4,711,691
Foreign Currency Exchange Contracts		—			15,275,771			—			15,275,771
Interest Rate Contracts		134,493,013			5,732,405			—			140,225,418
Unfunded Floating Rate Loan Interests(a)		—			4,603			—			4,603
Liabilities
TBA Sale Commitments		—			(7,004,095,321	)		—			(7,004,095,321	)
Unfunded Floating Rate Loan Interests (a)		—			—			(7,191	)		(7,191	)
	$	2,142,376,200		$	20,846,586,523		$	379,326,240			23,368,288,963
Investments Valued at NAV(b)											166,056,420
										$	23,534,345,383
Derivative Financial Instruments(c)
Assets
Credit Contracts	$	—		$	2,248,229		$	—		$	2,248,229
Equity Contracts		15,020			139,217			—			154,237
Foreign Currency Exchange Contracts		—			14,270,860			—			14,270,860
Interest Rate Contracts		43,964,558			20,089,939			—			64,054,497
Other Contracts		—			2,770,365			—			2,770,365
Liabilities
Credit Contracts		—			(6,094,527	)		—			(6,094,527	)
Equity Contracts		(2,069,509	)		(408,263	)		—			(2,477,772	)
Foreign Currency Exchange Contracts		—			(11,341,478	)		—			(11,341,478	)
Interest Rate Contracts		(151,963,891	)		(33,013,007	)		—			(184,976,898	)
Other Contracts		—			(9,631,655	)		—			(9,631,655	)
	$	(110,053,822	)	$	(20,970,320	)	$	—		$	(131,024,142	)

^(a)  Unfunded floating rate loan interests are valued at the unrealized appreciation (depreciation) on the commitment.

^(b)  Certain investments of the Master Portfolio were fair valued using NAV per share as no quoted market value is available and therefore have been excluded from the fair value hierarchy.

^(c)  Derivative financial instruments are swaps, futures contracts, forward foreign currency exchange contracts and options written. Swaps, futures contracts and forward foreign currency exchange contracts are valued at the unrealized appreciation (depreciation) on the instrument and options written are shown at value.

A reconciliation of Level 3 investments is presented when the Master Portfolio had a significant amount of Level 3 investments at the beginning and/or end of the period in relation to net assets. The following tables are a reconciliation of Level 3 investments for which significant unobservable inputs were used in determining fair value:

	Asset-Backed Securities			Common Stocks			Corporate Bonds			Floating Rate Loan Interests			Non-Agency Mortgage-Backed Securities
Assets
Opening Balance, as of September 30, 2020	$	185,886,590		$	282,627		$	38,948,734		$	133,453,277			$	21,820,080
Transfers into Level 3		5,157,143			—			351,214			—				—
Transfers out of Level 3		(71,869,916	)		—			(112,000	)		(5,999,730	)			(1,789,186	)
Accrued discounts/premiums		101,739			—			116,962			80,085				(68,700	)
Net realized gain (loss)		128,823			—			(131,732	)		609,738				89,045
Net change in unrealized appreciation (depreciation)(a)(b)		1,238,069			(51,878	)		7,732,675			6,305,554				145,261
Purchases		53,681,740			85,805			308,347			10,221,186				58,553,111
Sales		(10,657,786	)		(2,213	)		(12,339,211	)		(39,128,440	)			(4,594,457	)
Closing Balance, as of March 31, 2021	$	163,666,402		$	314,341		$	34,874,989		$	105,541,670			$	74,155,154
Net change in unrealized appreciation (depreciation) on investments still held at March 31, 2021(b)	$	902,602		$	(51,878	)	$	5,574,875		$	1,904,179			$	219,696

MASTER  PORTFOLIO    SCHEDULE   OF   INVESTMENTS 95

Schedule of Investments (unaudited) (continued) March 31, 2021 Master Total Return Portfolio

	Rights		Warrants			Unfunded Floating Rate Loan Interests				Total
Assets
Opening Balance, as of September 30, 2020	$	—	$	—			$	(14,194	)	$	380,377,114
Transfers into Level 3		—		—				—			5,508,357
Transfers out of Level 3		—		—				—			(79,770,832	)
Accrued discounts/premiums		—		—				—			230,086
Net realized gain (loss)		—		—				—			695,874
Net change in unrealized appreciation (depreciation)(a)(b)		—		(89,233	)			7,003			15,287,451
Purchases		321,840		548,268				—			123,720,297
Sales		—		—				—			(66,722,107	)
Closing Balance, as of March 31, 2021	$	321,840	$	459,035			$	(7,191	)	$	379,326,240
Net change in unrealized appreciation (depreciation) on investments still held at March 31, 2021(b)	$	—	$	(89,233	)		$	7,003		$	8,467,244

^(a)  Included in the related net change in unrealized appreciation (depreciation) in the Statement of Operations.

^(b)  Any difference between net change in unrealized appreciation (depreciation) and net change in unrealized appreciation (depreciation) on investments still held at March 31, 2021, is generally due to investments no longer held or categorized as Level 3 at period end.

The following table is a reconciliation of Level 3 derivative financial instruments for which significant unobservable inputs were used in determining fair value:

							Foreign Currency
	Credit Contracts						Exchange Contracts
	Assets			Liabilities			Assets		Liabilities
Opening Balance, as of September 30, 2020	$	960,974			$	—	$	—		$	(2	)
Transfers into Level 3		—				—		—			—
Transfers out of Level 3		(960,974	)			—		—			—
Accrued discounts/premiums		—				—		—			—
Net realized gain (loss)		—				—		—			—
Net change in unrealized appreciation (depreciation)(a)(b)		—				—		—			2
Purchases		—				—		—			—
Issues		—				—		—			—
Sales		—				—		—			—
Settlements		—				—		—			—
Closing Balance, as of March 31, 2021	$	—			$	—	$	—		$	—
Net change in unrealized appreciation (depreciation) on investments still held at March 31, 2021(b)	$	—			$	—	$	—		$	—

^(a)  Included in the related net change in unrealized appreciation (depreciation) in the Statement of Operations.

^(b)  Any difference between net change in unrealized appreciation (depreciation) and net change in unrealized appreciation (depreciation) on investments still held at March 31, 2021, is generally due to investments no longer held or categorized as Level 3 at period end.

See notes to financial statements.

96 2 0 2 1   BLACK ROCK  SEMI - ANNUAL  REPORT   TO  SHAREHOLDERS

Statement of Assets and Liabilities (unaudited)

March 31, 2021

	Master Total Return Portfolio
ASSETS
Investments at value — unaffiliated(a)(b)	$	28,529,748,424
Investments at value — affiliated(c)		2,008,694,868
Cash		7,270,069
Cash pledged:
Collateral — OTC derivatives		1,530,000
Collateral — TBA commitments		2,572,000
Futures contracts		66,670,010
Centrally cleared swaps		22,974,630
Foreign currency at value(d)		74,130,147
Receivables:
Investments sold		406,340,381
Options written		3,730,841
Securities lending income — affiliated		186,535
Swaps		342,228
TBA sale commitments		7,054,477,396
Capital shares sold		32,754,156
Dividends — affiliated		33,042
Interest — unaffiliated		141,387,636
Variation margin on futures contracts		4,193,678
Variation margin on centrally cleared swaps		1,552,141
Swap premiums paid		16,374,272
Unrealized appreciation on:
Forward foreign currency exchange contracts		14,582,735
OTC swaps		5,205,132
Unfunded floating rate loan interests		4,603
Prepaid expenses		195,141
Total assets		38,394,950,065
LIABILITIES
Cash received as collateral for OTC derivatives		32,320,520
Cash received as collateral for TBA commitments		5,163,000
Collateral on securities loaned at value		166,054,513
Options written at value(e)		102,183,528
TBA sale commitments at value(f)		7,004,095,321
Payables:
Investments purchased		9,991,635,872
Swaps		1,939,807
Investment advisory fees		860,714
Directors’ fees		64,950
Options written		8,921,851
Other accrued expenses		114,569
Other affiliate fees		101,445
Variation margin on futures contracts		8,172,329
Swap premiums received		3,006,612
Unrealized depreciation on:
Forward foreign currency exchange contracts		6,244,267
OTC swaps		7,330,442
Unfunded floating rate loan interests		7,191
Total liabilities		17,338,216,931
NET ASSETS	$	21,056,733,134

MASTER  PORTFOLIO  FINANCIAL    STATEMENTS 97

Statement of Assets and Liabilities (unaudited) (continued)

March 31, 2021

	Master Total Return Portfolio
NET ASSETS CONSIST OF
Investors’ capital	$	20,953,138,154
Net unrealized appreciation (depreciation)		103,594,980
NET ASSETS	$	21,056,733,134
(a) Investments at cost — unaffiliated	$	28,383,159,027
(b) Securities loaned at value	$	163,917,949
(c) Investments at cost — affiliated	$	2,008,695,373
(d) Foreign currency at cost	$	74,716,521
(e) Premiums received	$	37,897,867
(f) Proceeds from TBA sale commitments	$	7,054,477,396

See notes to financial statements.

98 2 0 2 1   BLACK ROCK  SEMI - ANNUAL  REPORT  TO  SHAREHOLDERS

Statement of Operations (unaudited)

Six Months Ended March 31, 2021

	Master Total Return Portfolio
INVESTMENT INCOME
Dividends — unaffiliated	$	1,333,155
Dividends — affiliated		4,261,569
Interest — unaffiliated		248,355,604
Securities lending income — affiliated — net		306,403
Foreign taxes withheld		(979,826	)
Total investment income		253,276,905
EXPENSES
Investment advisory		5,319,776
Accounting services		363,951
Custodian		300,718
Professional		109,194
Directors		77,077
Printing and postage		826
Miscellaneous		354,865
Total expenses excluding interest expense		6,526,407
Interest expense		84,302
Total expenses		6,610,709
Less:
Fees waived and/or reimbursed by the Manager		(248,973	)
Total expenses after fees waived and/or reimbursed		6,361,736
Net investment income		246,915,169
REALIZED AND UNREALIZED GAIN (LOSS)
Net realized gain (loss) from:
Investments — unaffiliated (net of $1,426 foreign capital gain tax)		179,789,321
Investments — affiliated		7,919,365
Options written		18,644,680
Futures contracts		(213,348,568	)
Forward foreign currency exchange contracts		(51,520,019	)
Foreign currency transactions		18,222,006
Swaps		(36,071,028	)
		(76,364,243	)
Net change in unrealized appreciation (depreciation) on:
Investments — unaffiliated		(231,927,207	)
Investments — affiliated		625,387
Options written		(67,538,033	)
Futures contracts		(16,769,206	)
Forward foreign currency exchange contracts		5,851,467
Foreign currency translations		(152,390	)
Swaps		(21,953,399	)
Unfunded floating rate loan interests		27,760
		(331,835,621	)
Net realized and unrealized loss		(408,199,864	)
NET DECREASE IN NET ASSETS RESULTING FROM OPERATIONS	$	(161,284,695	)

See notes to financial statements.

MASTER   PORTFOLIO   FINANCIAL   STATEMENTS 99

Statements of Changes in Net Assets

	Master Total Return Portfolio
	Six Months Ended 03/31/21 (unaudited)			Year Ended 09/30/20
INCREASE (DECREASE) IN NET ASSETS
OPERATIONS
Net investment income	$	246,915,169		$	480,285,925
Net realized gain (loss)		(76,364,243	)		824,425,976
Net change in unrealized appreciation (depreciation)		(331,835,621	)		35,793,461
Net increase (decrease) in net assets resulting from operations		(161,284,695	)		1,340,505,362
CAPITAL TRANSACTIONS
Proceeds from contributions		4,514,428,606			8,975,170,481
Value of withdrawals		(3,300,860,402	)		(6,024,057,622	)
Net increase in net assets derived from capital transactions		1,213,568,204			2,951,112,859
NET ASSETS
Total increase in net assets		1,052,283,509			4,291,618,221
Beginning of period		20,004,449,625			15,712,831,404
End of period	$	21,056,733,134		$	20,004,449,625

See notes to financial statements.

100 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Financial Highlights  

(For a share outstanding throughout each period)

		Master Total Return Portfolio
		Six Months Ended 03/31/21 (unaudited)
					Year Ended September 30,
						2020			2019	(a)		2018	(a)		2017	(a)		2016	(a)
Total Return
Total return			(0.65)	%(b)		7.90	%		10.60	%		(1.19	)%(c)		1.90	%		5.75	%
Ratios to Average Net Assets(d)
Total expenses			0.07	%(e)		0.07	%		0.07	%		0.34	%		0.32	%		0.21	%
Total expenses after fees waived and/or reimbursed			0.06	%(e)		0.06	%		0.07	%		0.34	%		0.32	%		0.21	%
Total expenses after fees waived and/or reimbursed and excluding interest expense			0.06	%(e)		0.06	%		0.07	%		0.07	%		0.08	%		0.08	%
Net investment income			2.44	%(e)		2.70	%		3.70	%		3.67	%		3.30	%		3.03	%
Supplemental Data
Net assets, end of period (000)		$	21,056,733			$ 20,004,450		$	15,712,831		$	13,063,847		$	11,601,109		$	9,309,960
Portfolio turnover rate(f)			241	%		556	%		574	%		734	%		806	%		841	%
(a) Consolidated Financial Highlights. (b) Aggregate total return. (c)  Includes a payment received from an affiliate, which had no impact on the Master Portfolio’s total return. (d) Excludes expenses incurred indirectly as a result of investments in underlying funds as follows:
		Six Months Ended 03/31/21 (unaudited)			Year Ended September 30,
					2020			2019			2018			2017			2016
	Investments in underlying funds		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%		0.01	%
(e) Annualized. (f)  Includes mortgage dollar roll transactions (“MDRs”). Additional information regarding portfolio turnover rate is as follows:
		Six Months Ended 03/31/21 (unaudited)			Year Ended September 30,
					2020			2019			2018			2017			2016
	Portfolio turnover rate (excluding MDRs)		86	%		274	%		241	%		350	%		540	%		598	%

See notes to financial statements.

FINANCIAL   HIGHLIGHTS 101

Notes to Financial Statements (unaudited)

1. ORGANIZATION

Master Total Return Portfolio (the “Master Portfolio”), a series of Master Bond LLC, is registered under the Investment Company Act of 1940, as amended (the “1940 Act”), as an open-end management investment company. The Master Bond LLC is organized as a Delaware limited liability company. The Master Portfolio is classified as diversified. The Limited Liability Company Agreement of the Master Bond LLC permits the Board of Directors of the Master Bond LLC (the “Board”) to issue non-transferable interests in the Master Bond LLC, subject to certain limitations.

The Master Portfolio, together with certain other registered investment companies advised by BlackRock Advisors, LLC (the “Manager”) or its affiliates, is included in a complex of non-index fixed-income mutual funds and all BlackRock-advised closed-end funds referred to as the BlackRock Fixed-Income Complex.

2. SIGNIFICANT ACCOUNTING POLICIES

The financial statements are prepared in conformity with accounting principles generally accepted in the United States of America (“U.S. GAAP”), which may require management to make estimates and assumptions that affect the reported amounts of assets and liabilities in the financial statements, disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of increases and decreases in net assets from operations during the reporting period. Actual results could differ from those estimates. The Master Portfolio is considered an investment company under U.S. GAAP and follows the accounting and reporting guidance applicable to investment companies. Below is a summary of significant accounting policies:

Investment Transactions and Income Recognition: For financial reporting purposes, investment transactions are recorded on the dates the transactions are executed. Realized gains and losses on investment transactions are determined using the specific identification method. Dividend income and capital gain distributions, if any, are recorded on the ex-dividend dates. Non-cash dividends, if any, are recorded on the ex-dividend dates at fair value. Dividends from foreign securities where the ex-dividend dates may have passed are subsequently recorded when the Master Portfolio is informed of the ex-dividend dates. Under the applicable foreign tax laws, a withholding tax at various rates may be imposed on capital gains, dividends and interest. Upon notification from issuers, a portion of the dividend income received from a real estate investment trust may be redesignated as a reduction of cost of the related investment and/or realized gain. Interest income, including amortization and accretion of premiums and discounts on debt securities, Funds with interest income from payment in-kind securities: and payment-in-kind interest are recognized daily on an accrual basis. For convertible securities, premiums attributable to the debt instrument are amortized, but premiums attributable to the conversion feature are not amortized.

Foreign Currency Translation: The Master Portfolio’s books and records are maintained in U.S. dollars. Securities and other assets and liabilities denominated in foreign currencies are translated into U.S. dollars using exchange rates determined as of the close of trading on the New York Stock Exchange (“NYSE”). Purchases and sales of investments are recorded at the rates of exchange prevailing on the respective dates of such transactions. Generally, when the U.S. dollar rises in value against a foreign currency, the investments denominated in that currency will lose value; the opposite effect occurs if the U.S. dollar falls in relative value.

The Master Portfolio does not isolate the effect of fluctuations in foreign exchange rates from the effect of fluctuations in the market prices of investments for financial reporting purposes. Accordingly, the effects of changes in exchange rates on investments are not segregated in the Statement of Operations from the effects of changes in market prices of those investments, but are included as a component of net realized and unrealized gain (loss) from investments. The Master Portfolio reports realized currency gains (losses) on foreign currency related transactions as components of net realized gain (loss) for financial reporting purposes, whereas such components are generally treated as ordinary income for U.S. federal income tax purposes.

Foreign Taxes: The Master Portfolio may be subject to foreign taxes (a portion of which may be reclaimable) on income, stock dividends, capital gains on investments,or certain foreign currency transactions. All foreign taxes are recorded in accordance with the applicable foreign tax regulations and rates that exist in the foreign jurisdictions in which the Master Portfolio invests. These foreign taxes, if any, are paid by the Master Portfolio and are reflected in its Statement of Operations as follows: foreign taxes withheld at source are presented as a reduction of income, foreign taxes on securities lending income are presented as a reduction of securities lending income, foreign taxes on stock dividends are presented as “Foreign taxes withheld”, and foreign taxes on capital gains from sales of investments and foreign taxes on foreign currency transactions are included in their respective net realized gain (loss) categories. Foreign taxes payable or deferred as of March 31, 2021, if any, are disclosed in the Statement of Assets and Liabilities.

The Master Portfolio files withholding tax reclaims in certain jurisdictions to recover a portion of amounts previously withheld. The Master Portfolio may record a reclaim receivable based on collectability, which includes factors such as the jurisdiction’s applicable laws, payment history and market convention. The Statement of Operations includes tax reclaims recorded as well as professional and other fees, if any, associated with recovery of foreign withholding taxes.

Segregation and Collateralization: In cases where the Master Portfolio enters into certain investments (e.g., to-be-announced (“TBA”) sale commitments, futures contracts, forward foreign currency exchange contracts, options written, swaps and structured options) that would be treated as “senior securities” for 1940 Act purposes, the Master Portfolio may segregate or designate on its books and records cash or liquid assets having a market value at least equal to the amount of its future obligations under such investments. Doing so allows the investment or borrowings to be excluded from treatment as a “senior security.” Furthermore, if required by an exchange or counterparty agreement, the Master Portfolio may be required to deliver/deposit cash and/or securities to/with an exchange, or broker-dealer or custodian as collateral for certain investments or obligations.

Deferred Compensation Plan: Under the Deferred Compensation Plan (the “Plan”) approved by the Master Portfolio’s Board, the directors who are not “interested persons” of the Master Bond LLC, as defined in the 1940 Act (“Independent Directors”), may defer a portion of their annual complex-wide compensation. Deferred amounts earn an approximate return as though equivalent dollar amounts had been invested in common shares of certain funds in the BlackRock Fixed-Income Complex selected by the Independent Directors. This has the same economic effect for the Independent Directors as if the Independent Directors had invested the deferred amounts directly in certain funds in the BlackRock Fixed-Income Complex.

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Notes to Financial Statements (unaudited) (continued)

The Plan is not funded and obligations thereunder represent general unsecured claims against the general assets of the Master Portfolio, as applicable. Deferred compensation liabilities, if any, are included in the Directors’ and Officer’s fees payable in the Statement of Assets and Liabilities and will remain as a liability of the Master Portfolio until such amounts are distributed in accordance with the Plan.

Indemnifications: In the normal course of business, the Master Portfolio enters into contracts that contain a variety of representations that provide general indemnification. The Master Portfolio’s maximum exposure under these arrangements is unknown because it involves future potential claims against the Master Portfolio, which cannot be predicted with any certainty.

Other: Expenses directly related to the Master Portfolio are charged to the Master Portfolio. Other operating expenses shared by several funds, including other funds managed by the Manager, are prorated among those funds on the basis of relative net assets or other appropriate methods.

The Master Portfolio has an arrangement with its custodian whereby credits are earned on uninvested cash balances, which could be used to reduce custody fees and/or overdraft charges. The Master Portfolio may incur charges on overdrafts, subject to certain conditions.

3. INVESTMENT VALUATION AND FAIR VALUE MEASUREMENTS

Investment Valuation Policies: The Master Portfolio’s investments are valued at fair value (also referred to as “market value” within the financial statements) each day that the Master Portfolio is open for business and, for financial reporting purposes, as of the report date. U.S. GAAP defines fair value as the price the Master Portfolio would receive to sell an asset or pay to transfer a liability in an orderly transaction between market participants at the measurement date. The Master Portfolio determines the fair values of its financial instruments using various independent dealers or pricing services under policies approved by the Board. If a security’s market price is not readily available or does not otherwise accurately represent the fair value of the security, the security will be valued in accordance with a policy approved by the Board as reflecting fair value. The BlackRock Global Valuation Methodologies Committee (the “Global Valuation Committee”) is the committee formed by management to develop global pricing policies and procedures and to oversee the pricing function for all financial instruments.

Fair Value Inputs and Methodologies: The following methods and inputs are used to establish the fair value of the Master Portfolio’s assets and liabilities:

• Equity investments traded on a recognized securities exchange are valued at that day’s official closing price, as applicable, on the exchange where the stock is primarily traded. Equity investments traded on a recognized exchange for which there were no sales on that day may be valued at the last available bid (long positions) or ask (short positions) price.

Generally, trading in foreign instruments is substantially completed each day at various times prior to the close of trading on the NYSE. Occasionally, events affecting the values of such instruments may occur between the foreign market close and the close of trading on the NYSE that may not be reflected in the computation of the Master Portfolio’s net assets. Each business day, the Master Portfolio uses a pricing service to assist with the valuation of certain foreign exchange-traded equity securities and foreign exchange-traded and over-the-counter (“OTC”) options (the “Systematic Fair Value Price”). Using current market factors, the Systematic Fair Value Price is designed to value such foreign securities and foreign options at fair value as of the close of trading on the NYSE, which follows the close of the local markets.

• Fixed-income investments for which market quotations are readily available are generally valued using the last available bid price or current market quotations provided by independent dealers or third party pricing services. Floating rate loan interests are valued at the mean of the bid prices from one or more independent brokers or dealers as obtained from a third party pricing service. Pricing services generally value fixed-income securities assuming orderly transactions of an institutional round lot size, but a fund may hold or transact in such securities in smaller, odd lot sizes. Odd lots may trade at lower prices than institutional round lots. The pricing services may use matrix pricing or valuation models that utilize certain inputs and assumptions to derive values, including transaction data (e.g., recent representative bids and offers), market data, credit quality information, perceived market movements, news, and other relevant information. Certain fixed-income securities, including asset-backed and mortgage related securities may be valued based on valuation models that consider the estimated cash flows of each tranche of the entity, establish a benchmark yield and develop an estimated tranche specific spread to the benchmark yield based on the unique attributes of the tranche. The amortized cost method of valuation may be used with respect to debt obligations with sixty days or less remaining to maturity unless the Manager determines such method does not represent fair value.

• Investments in open-end U.S. mutual funds (including money market funds) are valued at that day’s published net asset value (“NAV”).

• The Master Portfolio values its investment in SL Liquidity Series, LLC, Money Market Series (the “Money Market Series”) at fair value, which is ordinarily based upon its pro rata ownership in the underlying fund’s net assets.

• Futures contracts are valued based on that day’s last reported settlement or trade price on the exchange where the contract is traded.

• Forward foreign currency exchange contracts are valued at the mean between the bid and ask prices and are determined as of the close of trading on the NYSE based on that day’s prevailing forward exchange rate for the underlying currencies.

• Exchange-traded options are valued at the mean between the last bid and ask prices at the close of the options market in which the options trade. An exchange-traded option for which there is no mean price, is valued at the last bid (long positions) or ask (short positions) price. If no bid or ask price is available, the prior day’s price will be used, unless it is determined that the prior day’s price no longer reflects the fair value of the option. OTC options and options on swaps (“swaptions”) are valued by an independent pricing service using a mathematical model, which incorporates a number of market data factors, such as the trades and prices of the underlying instruments.

• Swap agreements are valued utilizing quotes received daily by independent pricing services or through brokers, which are derived using daily swap curves and models that incorporate a number of market data factors, such as discounted cash flows, trades and values of the underlying reference instruments.

If events (e.g., a market closure, market volatility, company announcement or a natural disaster) occur that are expected to materially affect the value of such investment, or in the event that application of these methods of valuation results in a price for an investment that is deemed not to be representative of the market value of such investment, or if a price is not available, the investment will be valued by the Global Valuation Committee, or its delegate, in accordance with a policy approved by the Board as reflecting

NOTES   TO   FINANCIAL   STATEMENTS 103

Notes to Financial Statements (unaudited) (continued)

fair value (“Fair Valued Investments”). The fair valuation approaches that may be used by the Global Valuation Committee include market approach, income approach and cost approach. Valuation techniques such as discounted cash flow, use of market comparables and matrix pricing are types of valuation approaches and are typically used in determining fair value. When determining the price for Fair Valued Investments, the Global Valuation Committee, or its delegate, seeks to determine the price that the Master Portfolio might reasonably expect to receive or pay from the current sale or purchase of that asset or liability in an arm’s-length transaction. Fair value determinations shall be based upon all available factors that the Global Valuation Committee, or its delegate, deems relevant and consistent with the principles of fair value measurement. The pricing of all Fair Valued Investments is subsequently reported to the Board or a committee thereof on a quarterly basis.

For investments in equity or debt issued by privately held companies or funds (“Private Company” or collectively, the “Private Companies”) and other Fair Valued Investments, the fair valuation approaches that are used by the Global Valuation Committee and third party pricing services utilize one or a combination of, but not limited to, the following inputs.

Standard Inputs Generally Considered By Third Party Pricing Services
Market approach	(i)	recent market transactions, including subsequent rounds of financing, in the underlying investment or comparable issuers;
	(ii)	recapitalizations and other transactions across the capital structure; and
	(iii)	market multiples of comparable issuers.
Income approach	(i)	future cash flows discounted to present and adjusted as appropriate for liquidity, credit and/or market risks;
	(ii)	quoted prices for similar investments or assets in active markets; and
	(iii)	other risk factors, such as interest rates, yield curves, volatilities, prepayment speeds, loss severities, credit risks, recovery rates, liquidation amounts and/or default rates.
Cost approach	(i)	audited or unaudited financial statements, investor communications and financial or operational metrics issued by the Private Company;
	(ii)	changes in the valuation of relevant indices or publicly traded companies comparable to the Private Company;
	(iii)	relevant news and other public sources; and
	(iv)	known secondary market transactions in the Private Company’s interests and merger or acquisition activity in companies comparable to the Private Company.

Investments in series of preferred stock issued by Private Companies are typically valued utilizing market approach in determining the enterprise value of the company. Such investments often contain rights and preferences that differ from other series of preferred and common stock of the same issuer. Enterprise valuation techniques such as an option pricing model (“OPM”), a probability weighted expected return model (“PWERM”), current value method or a hybrid of those techniques are used, as deemed appropriate under the circumstances. The use of these valuation techniques involve a determination of the exit scenarios of the investment in order to appropriately allocate the enterprise value of the company among the various parts of its capital structure.

The Private Companies are not subject to the public company disclosure, timing, and reporting standards applicable to other investments held by the Master Portfolio. Typically, the most recently available information by a Private Company is as of a date that is earlier than the date the Master Portfolio is calculating its NAV. This factor may result in a difference between the value of the investment and the price the Master Portfolio could receive upon the sale of the investment.

Fair Value Hierarchy: Various inputs are used in determining the fair value of financial instruments. These inputs to valuation techniques are categorized into a fair value hierarchy consisting of three broad levels for financial reporting purposes as follows:

• Level 1 – Unadjusted price quotations in active markets/exchanges for identical assets or liabilities that the Master Portfolio has the ability to access;

• Level 2 – Other observable inputs (including, but not limited to, quoted prices for similar assets or liabilities in markets that are active, quoted prices for identical or similar assets or liabilities in markets that are not active, inputs other than quoted prices that are observable for the assets or liabilities (such as interest rates, yield curves, volatilities, prepayment speeds, loss severities, credit risks and default rates) or other market–corroborated inputs); and

• Level 3 – Unobservable inputs based on the best information available in the circumstances, to the extent observable inputs are not available (including the Global Valuation Committee’s assumptions used in determining the fair value of financial instruments).

The hierarchy gives the highest priority to unadjusted quoted prices in active markets for identical assets or liabilities (Level 1 measurements) and the lowest priority to unobservable inputs (Level 3 measurements). Accordingly, the degree of judgment exercised in determining fair value is greatest for instruments categorized in Level 3. The inputs used to measure fair value may fall into different levels of the fair value hierarchy. In such cases, for disclosure purposes, the fair value hierarchy classification is determined based on the lowest level input that is significant to the fair value measurement in its entirety. Investments classified within Level 3 have significant unobservable inputs used by the Global Valuation Committee in determining the price for Fair Valued Investments. Level 3 investments include equity or debt issued by Private Companies that may not have a secondary market and/or may have a limited number of investors. The categorization of a value determined for financial instruments is based on the pricing transparency of the financial instruments and is not necessarily an indication of the risks associated with investing in those securities.

As of March 31, 2021, certain investments of the Master Portfolio were fair valued using NAV per share as no quoted market value is available and therefore have been excluded from the fair value hierarchy.

4. SECURITIES AND OTHER INVESTMENTS

Asset-Backed and Mortgage-Backed Securities: Asset-backed securities are generally issued as pass-through certificates or as debt instruments. Asset-backed securities issued as pass-through certificates represent undivided fractional ownership interests in an underlying pool of assets. Asset-backed securities issued as debt instruments, which are also known as collateralized obligations, are typically issued as the debt of a special purpose entity organized solely for the purpose of owning such assets and

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Notes to Financial Statements (unaudited) (continued)

issuing such debt. Asset-backed securities are often backed by a pool of assets representing the obligations of a number of different parties. The yield characteristics of certain asset-backed securities may differ from traditional debt securities. One such major difference is that all or a principal part of the obligations may be prepaid at any time because the underlying assets (i.e., loans) may be prepaid at any time. As a result, a decrease in interest rates in the market may result in increases in the level of prepayments as borrowers, particularly mortgagors, refinance and repay their loans. An increased prepayment rate with respect to an asset-backed security will have the effect of shortening the maturity of the security. In addition, the Master Portfolio may subsequently have to reinvest the proceeds at lower interest rates. If the Master Portfolio has purchased such an asset-backed security at a premium, a faster than anticipated prepayment rate could result in a loss of principal to the extent of the premium paid.

For mortgage pass-through securities (the “Mortgage Assets”) there are a number of important differences among the agencies and instrumentalities of the U.S. Government that issue mortgage-related securities and among the securities that they issue. For example, mortgage-related securities guaranteed by Ginnie Mae are guaranteed as to the timely payment of principal and interest by Ginnie Mae and such guarantee is backed by the full faith and credit of the United States. However, mortgage-related securities issued by Freddie Mac and Fannie Mae, including Freddie Mac and Fannie Mae guaranteed mortgage pass-through certificates, which are solely the obligations of Freddie Mac and Fannie Mae, are not backed by or entitled to the full faith and credit of the United States, but are supported by the right of the issuer to borrow from the U.S. Treasury.

Non-agency mortgage-backed securities are securities issued by non-governmental issuers and have no direct or indirect government guarantees of payment and are subject to various risks. Non-agency mortgage loans are obligations of the borrowers thereunder only and are not typically insured or guaranteed by any other person or entity. The ability of a borrower to repay a loan is dependent upon the income or assets of the borrower. A number of factors, including a general economic downturn, acts of God, terrorism, social unrest and civil disturbances, may impair a borrower’s ability to repay its loans.

Collateralized Debt Obligations: Collateralized debt obligations (“CDOs”), including collateralized bond obligations (“CBOs”) and collateralized loan obligations (“CLOs”), are types of asset-backed securities. ACDO is an entity that is backed by a diversified pool of debt securities (CBOs) or syndicated bank loans (CLOs). The cash flows of the CDO can be split into multiple segments, called “tranches,” which will vary in risk profile and yield. The riskiest segment is the subordinated or “equity” tranche. This tranche bears the greatest risk of defaults from the underlying assets in the CDO and serves to protect the other, more senior, tranches from default in all but the most severe circumstances. Since it is shielded from defaults by the more junior tranches, a “senior” tranche will typically have higher credit ratings and lower yields than their underlying securities, and often receive investment grade ratings from one or more of the nationally recognized rating agencies. Despite the protection from the more junior tranches, senior tranches can experience substantial losses due to actual defaults, increased sensitivity to future defaults and the disappearance of one or more protecting tranches as a result of changes in the credit profile of the underlying pool of assets.

Inflation-Indexed Bonds: Inflation-indexed bonds (other than municipal inflation-indexed and certain corporate inflation-indexed bonds) are fixed-income securities whose principal value is periodically adjusted according to the rate of inflation. If the index measuring inflation rises or falls, the principal value of inflation-indexed bonds (other than municipal inflation-indexed and certain corporate inflation-indexed bonds) will be adjusted upward or downward, and consequently the interest payable on these securities (calculated with respect to a larger or smaller principal amount) will be increased or reduced, respectively. Any upward or downward adjustment in the principal amount of an inflation-indexed bond is included as interest income in the Statement of Operations, even though investors do not receive their principal until maturity. Repayment of the original bond principal upon maturity (as adjusted for inflation) is guaranteed in the case of U.S. Treasury inflation-indexed bonds. For bonds that do not provide a similar guarantee, the adjusted principal value of the bond repaid at maturity may be less than the original principal. With regard to municipal inflation-indexed bonds and certain corporate inflation-indexed bonds, the inflation adjustment is typically reflected in the semi-annual coupon payment. As a result, the principal value of municipal inflation-indexed bonds and such corporate inflation-indexed bonds does not adjust according to the rate of inflation.

Multiple Class Pass-Through Securities: Multiple class pass-through securities, including collateralized mortgage obligations (“CMOs”) and commercial mortgage-backed securities, may be issued by Ginnie Mae, U.S. Government agencies or instrumentalities or by trusts formed by private originators of, or investors in, mortgage loans. In general, CMOs are debt obligations of a legal entity that are collateralized by a pool of residential or commercial mortgage loans or Mortgage Assets. The payments on these are used to make payments on the CMOs or multiple pass-through securities. Multiple class pass-through securities represent direct ownership interests in the Mortgage Assets. Classes of CMOs include interest only (“IOs”), principal only (“POs”), planned amortization classes and targeted amortization classes. IOs and POs are stripped mortgage-backed securities representing interests in a pool of mortgages, the cash flow from which has been separated into interest and principal components. IOs receive the interest portion of the cash flow while POs receive the principal portion. IOs and POs can be extremely volatile in response to changes in interest rates. As interest rates rise and fall, the value of IOs tends to move in the same direction as interest rates. POs perform best when prepayments on the underlying mortgages rise since this increases the rate at which the principal is returned and the yield to maturity on the PO. When payments on mortgages underlying a PO are slower than anticipated, the life of the PO is lengthened and the yield to maturity is reduced. If the underlying Mortgage Assets experience greater than anticipated prepayments of principal, the Master Portfolio’s initial investment in the IOs may not fully recoup.

Stripped Mortgage-Backed Securities: Stripped mortgage-backed securities are typically issued by the U.S. Government, its agencies and instrumentalities. Stripped mortgage-backed securities are usually structured with two classes that receive different proportions of the interest (IOs) and principal (POs) distributions on a pool of Mortgage Assets. Stripped mortgage-backed securities may be privately issued.

Zero-Coupon Bonds: Zero-coupon bonds are normally issued at a significant discount from face value and do not provide for periodic interest payments. These bonds may experience greater volatility in market value than other debt obligations of similar maturity which provide for regular interest payments.

Capital Securities and Trust Preferred Securities: Capital securities, including trust preferred securities, are typically issued by corporations, generally in the form of interest-bearing notes with preferred securities characteristics. In the case of trust preferred securities, an affiliated business trust of a corporation issues these securities, generally in the form of beneficial interests in subordinated debentures or similarly structured securities. The securities can be structured with either a fixed or adjustable coupon that can have either a perpetual or stated maturity date. For trust preferred securities, the issuing bank or corporation pays interest to the trust, which is then distributed to holders of these securities as a dividend. Dividends can be deferred without creating an event of default or acceleration, although maturity cannot take place unless all cumulative payment obligations have been met. The deferral of payments does not affect the purchase or sale of these securities in the open market. These securities generally are rated below that of the issuing company’s senior debt securities and are freely callable at the issuer’s option.

NOTES   TO   FINANCIAL   STATEMENTS 105

Notes to Financial Statements (unaudited) (continued)

Preferred Stocks: Preferred stock has a preference over common stock in liquidation (and generally in receiving dividends as well), but is subordinated to the liabilities of the issuer in all respects. As a general rule, the market value of preferred stock with a fixed dividend rate and no conversion element varies inversely with interest rates and perceived credit risk, while the market price of convertible preferred stock generally also reflects some element of conversion value. Because preferred stock is junior to debt securities and other obligations of the issuer, deterioration in the credit quality of the issuer will cause greater changes in the value of a preferred stock than in a more senior debt security with similar stated yield characteristics. Unlike interest payments on debt securities, preferred stock dividends are payable only if declared by the issuer’s board of directors. Preferred stock also may be subject to optional or mandatory redemption provisions.

Floating Rate Loan Interests: Floating rate loan interests are typically issued to companies (the “borrower”) by banks, other financial institutions, or privately and publicly offered corporations (the “lender”). Floating rate loan interests are generally non-investment grade, often involve borrowers whose financial condition is troubled or uncertain and companies that are highly leveraged or in bankruptcy proceedings. In addition, transactions in floating rate loan interests may settle on a delayed basis, which may result in proceeds from the sale not being readily available for a fund to make additional investments or meet its redemption obligations. Floating rate loan interests may include fully funded term loans or revolving lines of credit. Floating rate loan interests are typically senior in the corporate capital structure of the borrower. Floating rate loan interests generally pay interest at rates that are periodically determined by reference to a base lending rate plus a premium. Since the rates reset only periodically, changes in prevailing interest rates (and particularly sudden and significant changes) can be expected to cause some fluctuations in the NAV of a fund to the extent that it invests in floating rate loan interests. The base lending rates are generally the lending rate offered by one or more European banks, such as the London Interbank Offered Rate (“LIBOR”), the prime rate offered by one or more U.S. banks or the certificate of deposit rate. Floating rate loan interests may involve foreign borrowers, and investments may be denominated in foreign currencies. These investments are treated as investments in debt securities for purposes of a fund’s investment policies.

When a fund purchases a floating rate loan interest, it may receive a facility fee and when it sells a floating rate loan interest, it may pay a facility fee. On an ongoing basis, a fund may receive a commitment fee based on the undrawn portion of the underlying line of credit amount of a floating rate loan interest. Facility and commitment fees are typically amortized to income over the term of the loan or term of the commitment, respectively. Consent and amendment fees are recorded to income as earned. Prepayment penalty fees, which may be received by a fund upon the prepayment of a floating rate loan interest by a borrower, are recorded as realized gains. A fund may invest in multiple series or tranches of a loan. A different series or tranche may have varying terms and carry different associated risks.

Floating rate loan interests are usually freely callable at the borrower’s option. A fund may invest in such loans in the form of participations in loans (“Participations”) or assignments (“Assignments”) of all or a portion of loans from third parties. Participations typically will result in a fund having a contractual relationship only with the lender, not with the borrower. A fund has the right to receive payments of principal, interest and any fees to which it is entitled only from the lender selling the Participation and only upon receipt by the lender of the payments from the borrower. In connection with purchasing Participations, a fund generally will have no right to enforce compliance by the borrower with the terms of the loan agreement, nor any rights of offset against the borrower. A fund may not benefit directly from any collateral supporting the loan in which it has purchased the Participation. As a result, a fund assumes the credit risk of both the borrower and the lender that is selling the Participation. A fund’s investment in loan participation interests involves the risk of insolvency of the financial intermediaries who are parties to the transactions. In the event of the insolvency of the lender selling the Participation, a fund may be treated as a general creditor of the lender and may not benefit from any offset between the lender and the borrower. Assignments typically result in a fund having a direct contractual relationship with the borrower, and a fund may enforce compliance by the borrower with the terms of the loan agreement.

In connection with floating rate loan interests, the Master Portfolio may also enter into unfunded floating rate loan interests (“commitments”). In connection with these commitments, the Master Portfolio earns a commitment fee, typically set as a percentage of the commitment amount. Such fee income, which is included in interest income in the Statement of Operations, is recognized ratably over the commitment period. Unfunded floating rate loan interests are marked-to-market daily, and any unrealized appreciation (depreciation) is included in the Statement of Assets and Liabilities and Statement of Operations. As of period end, the Master Portfolio had the following unfunded floating rate loan interests:

Borrower	Par		Commitment Amount		Value		Unrealized Appreciation (Depreciation)
Amazon Logistics, Term Loan	$	38,203,076	$	38,198,473	$	38,203,076		$  4,603
BRE Park Avenue Tower Owner LLC, Mezzanine A Loan		528,064		528,064		528,011		(53	)
BSREP II Houston Office 1HC Owner LLC, Mezzanine Loan		2,312,819		2,312,819		2,307,268		(5,551	)
Burlingame Point LLC, Construction Loan		5,130,513		5,132,101		5,130,514		(1,587	)

Forward Commitments, When-Issued and Delayed Delivery Securities: The Master Portfolio may purchase securities on a when-issued basis and may purchase or sell securities on a forward commitment basis. Settlement of such transactions normally occurs within a month or more after the purchase or sale commitment is made. The Master Portfolio may purchase securities under such conditions with the intention of actually acquiring them, but may enter into a separate agreement to sell the securities before the settlement date. Since the value of securities purchased may fluctuate prior to settlement, the Master Portfolio may be required to pay more at settlement than the security is worth. In addition, the Master Portfolio is not entitled to any of the interest earned prior to settlement. When purchasing a security on a delayed delivery basis, the Master Portfolio assumes the rights and risks of ownership of the security, including the risk of price and yield fluctuations. In the event of default by the counterparty, the Master Portfolio’s maximum amount of loss is the unrealized appreciation of unsettled when-issued transactions.

TBA Commitments: TBA commitments are forward agreements for the purchase or sale of securities, including mortgage-backed securities for a fixed price, with payment and delivery on an agreed upon future settlement date. The specific securities to be delivered are not identified at the trade date. However, delivered securities must meet specified terms, including issuer, rate and mortgage terms. When entering into TBA commitments, the Master Portfolio may take possession of or deliver the underlying mortgage-backed securities but can extend the settlement or roll the transaction. TBA commitments involve a risk of loss if the value of the security to be purchased or sold declines or increases, respectively, prior to settlement date, if there are expenses or delays in connection with the TBA transactions, or if the counterparty fails to complete the transaction.

106 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Notes to Financial Statements (unaudited) (continued)

In order to better define contractual rights and to secure rights that will help the Master Portfolio mitigate its counterparty risk, TBA commitments may be entered into by the Master Portfolio under Master Securities Forward Transaction Agreements (each, an “MSFTA”). An MSFTA typically contains, among other things, collateral posting terms and netting provisions in the event of default and/or termination event. The collateral requirements are typically calculated by netting the mark-to-market amount for each transaction under such agreement and comparing that amount to the value of the collateral currently pledged by the Master Portfolio and the counterparty. Cash collateral that has been pledged to cover the obligations of the Master Portfolio and cash collateral received from the counterparty, if any, is reported separately in the Statement of Assets and Liabilities as cash pledged as collateral for TBA commitments or cash received as collateral for TBA commitments, respectively. Non-cash collateral pledged by the Master Portfolio, if any, is noted in the Schedule of Investments. Typically, the Master Portfolio is permitted to sell, re-pledge or use the collateral it receives; however, the counterparty is not permitted to do so. To the extent amounts due to the Master Portfolio are not fully collateralized, contractually or otherwise, the Master Portfolio bears the risk of loss from counterparty non-performance.

Mortgage Dollar Roll Transactions: The Master Portfolio may sell TBA mortgage-backed securities and simultaneously contract to repurchase substantially similar (i.e., same type, coupon and maturity) securities on a specific future date at an agreed upon price. During the period between the sale and repurchase, a fund is not entitled to receive interest and principal payments on the securities sold. Mortgage dollar roll transactions are treated as purchases and sales and a fund realizes gains and losses on these transactions. Mortgage dollar rolls involve the risk that the market value of the securities that a fund is required to purchase may decline below the agreed upon repurchase price of those securities.

Reverse Repurchase Agreements: Reverse repurchase agreements are agreements with qualified third party broker dealers in which the Master Portfolio sells securities to a bank or broker-dealer and agrees to repurchase the same securities at a mutually agreed upon date and price. The Master Portfolio receives cash from the sale to use for other investment purposes. During the term of the reverse repurchase agreement, the Master Portfolio continues to receive the principal and interest payments on the securities sold. Certain agreements have no stated maturity and can be terminated by either party at any time. Interest on the value of the reverse repurchase agreements issued and outstanding is based upon competitive market rates determined at the time of issuance. The Master Portfolio may utilize reverse repurchase agreements when it is anticipated that the interest income to be earned from the investment of the proceeds of the transaction is greater than the interest expense of the transaction. Reverse repurchase agreements involve leverage risk. If the Master Portfolio suffers a loss on its investment of the transaction proceeds from a reverse repurchase agreement, the Master Portfolio would still be required to pay the full repurchase price. Further, the Master Portfolio remains subject to the risk that the market value of the securities repurchased declines below the repurchase price. In such cases, the Master Portfolio would be required to return a portion of the cash received from the transaction or provide additional securities to the counterparty.

Cash received in exchange for securities delivered plus accrued interest due to the counterparty is recorded as a liability in the Statement of Assets and Liabilities at face value including accrued interest. Due to the short-term nature of the reverse repurchase agreements, face value approximates fair value. Interest payments made by the Master Portfolio to the counterparties are recorded as a component of interest expense in the Statement of Operations. In periods of increased demand for the security, the Master Portfolio may receive a fee for the use of the security by the counterparty, which may result in interest income to the Master Portfolio.

For the six months ended March 31, 2021, the average amount of reverse repurchase agreements outstanding was $116,103,220 and the daily weighted average interest rate was 0.14%.

Reverse repurchase transactions are entered into by the Master Portfolio under Master Repurchase Agreements (each, an “MRA”), which permit the Master Portfolio, under certain circumstances, including an event of default (such as bankruptcy or insolvency), to offset payables and/or receivables under the MRA with collateral held and/or posted to the counterparty and create one single net payment due to or from the Master Portfolio. With reverse repurchase transactions, typically the Master Portfolio and counterparty under an MRA are permitted to sell, re-pledge, or use the collateral associated with the transaction. Bankruptcy or insolvency laws of a particular jurisdiction may impose restrictions on or prohibitions against such a right of offset in the event of the MRA counterparty’s bankruptcy or insolvency. Pursuant to the terms of the MRA, the Master Portfolio receives or posts securities and cash as collateral with a market value in excess of the repurchase price to be paid or received by the Master Portfolio upon the maturity of the transaction. Upon a bankruptcy or insolvency of the MRA counterparty, the Master Portfolio is considered an unsecured creditor with respect to excess collateral and, as such, the return of excess collateral may be delayed.

Commitments: Commitments are agreements to acquire an investment at a future date (subject to conditions) in connection with a potential public or non-public offering. Such agreements may obligate the Master Portfolio to make future cash payments. As of March 31, 2021, the Master Portfolio had outstanding commitments of $118,864,210. These commitments are not included in the net assets of the Master Portfolio as of March 31, 2021.

Securities Lending: The Master Portfolio may lend its securities to approved borrowers, such as brokers, dealers and other financial institutions. The borrower pledges and maintains with the Master Portfolio collateral consisting of cash, an irrevocable letter of credit issued by a bank, or securities issued or guaranteed by the U.S. Government. The initial collateral received by the Master Portfolio is required to have a value of at least 102% of the current value of the loaned securities for securities traded on U.S. exchanges and a value of at least 105% for all other securities. The collateral is maintained thereafter at a value equal to at least 100% of the current market value of the securities on loan. The market value of the loaned securities is determined at the close of each business day of the Master Portfolio and any additional required collateral is delivered to the Master Portfolio, or excess collateral returned by the Master Portfolio, on the next business day. During the term of the loan, the Master Portfolio is entitled to all distributions made on or in respect of the loaned securities, but does not receive interest income on securities received as collateral. Loans of securities are terminable at any time and the borrower, after notice, is required to return borrowed securities within the standard time period for settlement of securities transactions.

As of period end, any securities on loan were collateralized by cash and/or U.S. Government obligations. Cash collateral invested by the securities lending agent, BlackRock Investment Management, LLC (“BIM”), if any, is disclosed in the Schedule of Investments. Any non-cash collateral received cannot be sold, re-invested or pledged by the Master Portfolio, except in the event of borrower default. The securities on loan, if any, are disclosed in the Master Portfolio’s Schedule of Investments. The market value of any securities on loan and the value of any related collateral are shown separately in the Statement of Assets and Liabilities as a component of investments at value – unaffiliated and collateral on securities loaned at value, respectively.

NOTES   TO   FINANCIAL   STATEMENTS 107

Notes to Financial Statements (unaudited) (continued)

Securities lending transactions are entered into by the Master Portfolio under Master Securities Lending Agreements (each, an “MSLA”), which provide the right, in the event of default (including bankruptcy or insolvency), for the non-defaulting party to liquidate the collateral and calculate a net exposure to the defaulting party or request additional collateral. In the event that a borrower defaults, the Master Portfolio, as lender, would offset the market value of the collateral received against the market value of the securities loaned. When the value of the collateral is greater than that of the market value of the securities loaned, the lender is left with a net amount payable to the defaulting party. However, bankruptcy or insolvency laws of a particular jurisdiction may impose restrictions on or prohibitions against such a right of offset in the event of an MSLA counterparty’s bankruptcy or insolvency. Under the MSLA, absent an event of default, the borrower can resell or re-pledge the loaned securities, and the Master Portfolio can reinvest cash collateral received in connection with loaned securities. Upon an event of default, the parties’ obligations to return the securities or collateral to the other party are extinguished, and the parties can resell or re-pledge the loaned securities or the collateral received in connection with the loaned securities in order to satisfy the defaulting party’s net payment obligation for all transactions under the MSLA. The defaulting party remains liable for any deficiency.

As of period end, the following table is a summary of the Master Portfolio’s securities on loan by counterparty which are subject to offset under an MSLA:

	Securities				Cash					Net
Counterparty		Loaned at Value				Collateral Received(a)					Amount	(b)
BNP Paribas Securities Corp.				$ 12,223,440			$	(12,223,440	)		$ —
BofA Securities, Inc.				2,754,700				(2,730,000	)		24,700
Credit Suisse Securities (USA) LLC				2,458,040				(2,430,200	)		27,840
Deutsche Bank Securities, Inc.				11,768				(11,768	)		—
Goldman Sachs & Co.				46,452,049				(46,452,049	)		—
J.P. Morgan Securities LLC				2,284,116				(2,284,116	)		—
SG Americas Securities LLC				97,733,836				(97,733,836	)		—
			$	163,917,949			$	(163,865,409	)	$	52,540

^(a)  Collateral received in excess of the market value of securities on loan is not presented in this table. The total cash collateral received by the Master Portfolio is disclosed in the Master Portfolio’s Statement of Assets and Liabilities.

^(b)  The market value of the loaned securities is determined as of March 31, 2021. Additional collateral is delivered to the Master Portfolio on the next business day in accordance with the MSLA. The net amount would be subject to the borrower default indemnity in the event of default by the counterparty.

The risks of securities lending include the risk that the borrower may not provide additional collateral when required or may not return the securities when due. To mitigate these risks, the Master Portfolio benefits from a borrower default indemnity provided by BIM. BIM’s indemnity allows for full replacement of the securities loaned to the extent the collateral received does not cover the value on the securities loaned in the event of borrower default. The Master Portfolio could incur a loss if the value of an investment purchased with cash collateral falls below the market value of loaned securities or if the value of an investment purchased with cash collateral falls below the value of the original cash collateral received. Such losses are borne entirely by the Master Portfolio.

5. DERIVATIVE FINANCIAL INSTRUMENTS

The Master Portfolio engages in various portfolio investment strategies using derivative contracts both to increase the returns of the Master Portfolio and/or to manage its exposure to certain risks such as credit risk, equity risk, interest rate risk, foreign currency exchange rate risk, commodity price risk or other risks (e.g., inflation risk). Derivative financial instruments categorized by risk exposure are included in the Schedule of Investments. These contracts may be transacted on an exchange or OTC.

Futures Contracts: Futures contracts are purchased or sold to gain exposure to, or manage exposure to, changes in interest rates (interest rate risk) and changes in the value of equity securities (equity risk) or foreign currencies (foreign currency exchange rate risk).

Futures contracts are exchange-traded agreements between the Master Portfolio and a counterparty to buy or sell a specific quantity of an underlying instrument at a specified price and on a specified date. Depending on the terms of a contract, it is settled either through physical delivery of the underlying instrument on the settlement date or by payment of a cash amount on the settlement date. Upon entering into a futures contract, the Master Portfolio is required to deposit initial margin with the broker in the form of cash or securities in an amount that varies depending on a contract’s size and risk profile. The initial margin deposit must then be maintained at an established level over the life of the contract. Amounts pledged, which are considered restricted, are included in cash pledged for futures contracts in the Statement of Assets and Liabilities.

Securities deposited as initial margin are designated in the Schedule of Investments and cash deposited, if any, are shown as cash pledged for futures contracts in the Statement of Assets and Liabilities. Pursuant to the contract, the Master Portfolio agrees to receive from or pay to the broker an amount of cash equal to the daily fluctuation in market value of the contract (“variation margin”). Variation margin is recorded as unrealized appreciation (depreciation) and, if any, shown as variation margin receivable (or payable) on futures contracts in the Statement of Assets and Liabilities. When the contract is closed, a realized gain or loss is recorded in the Statement of Operations equal to the difference between the notional amount of the contract at the time it was opened and the notional amount at the time it was closed. The use of futures contracts involves the risk of an imperfect correlation in the movements in the price of futures contracts and interest rates, foreign currency exchange rates or underlying assets.

Forward Foreign Currency Exchange Contracts: Forward foreign currency exchange contracts are entered into to gain or reduce exposure to foreign currencies (foreign currency exchange rate risk).

A forward foreign currency exchange contract is an agreement between two parties to buy and sell a currency at a set exchange rate on a specified date. These contracts help to manage the overall exposure to the currencies in which some of the investments held by the Master Portfolio are denominated and in some cases, may be used to obtain exposure to a particular market. The contracts are traded OTC and not on an organized exchange.

108 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Notes to Financial Statements (unaudited) (continued)

The contract is marked-to-market daily and the change in market value is recorded as unrealized appreciation (depreciation) in the Statement of Assets and Liabilities. When a contract is closed, a realized gain or loss is recorded in the Statement of Operations equal to the difference between the value at the time it was opened and the value at the time it was closed. Non-deliverable forward foreign currency exchange contracts are settled with the counterparty in cash without the delivery of foreign currency. The use of forward foreign currency exchange contracts involves the risk that the value of a forward foreign currency exchange contract changes unfavorably due to movements in the value of the referenced foreign currencies, and such value may exceed the amounts reflected in the Statement of Assets and Liabilities. Cash amounts pledged for forward foreign currency exchange contracts are considered restricted and are included in cash pledged as collateral for OTC derivatives in the Statement of Assets and Liabilities. The Master Portfolio’s risk of loss from counterparty credit risk on OTC derivatives is generally limited to the aggregate unrealized gain netted against any collateral held by the Master Portfolio.

Options: The Master Portfolio may purchase and write call and put options to increase or decrease its exposure to the risks of underlying instruments, including equity risk, interest rate risk and/or commodity price risk and/or, in the case of options written, to generate gains from options premiums.

A call option gives the purchaser (holder) of the option the right (but not the obligation) to buy, and obligates the seller (writer) to sell (when the option is exercised) the underlying instrument at the exercise or strike price at any time or at a specified time during the option period. A put option gives the holder the right to sell and obligates the writer to buy the underlying instrument at the exercise or strike price at any time or at a specified time during the option period.

Premiums paid on options purchased and premiums received on options written, as well as the daily fluctuation in market value, are included in investments at value –unaffiliated and options written at value, respectively, in the Statement of Assets and Liabilities. When an instrument is purchased or sold through the exercise of an option, the premium is offset against the cost or proceeds of the underlying instrument. When an option expires, a realized gain or loss is recorded in the Statement of Operations to the extent of the premiums received or paid. When an option is closed or sold, a gain or loss is recorded in the Statement of Operations to the extent the cost of the closing transaction exceeds the premiums received or paid. When the Master Portfolio writes a call option, such option is typically “covered,” meaning that it holds the underlying instrument subject to being called by the option counterparty. When the Master Portfolio writes a put option, cash is segregated in an amount sufficient to cover the obligation. These amounts, which are considered restricted, are included in cash pledged as collateral for options written in the Statement of Assets and Liabilities.

• Swaptions – The Master Portfolio may purchase and write swaptions primarily to preserve a return or spread on a particular investment or portion of the Master Portfolio’s holdings, as a duration management technique or to protect against an increase in the price of securities it anticipates purchasing at a later date. The purchaser and writer of a swaption is buying or granting the right to enter into a previously agreed upon interest rate or credit default swap agreement (interest rate risk and/or credit risk) at any time before the expiration of the option.

• Interest rate caps and floors – Interest rate caps and floors are entered into to gain or reduce exposure to interest rates (interest rate risk and/or other risk). Caps are agreements whereby one party agrees to make payments to the other, in return for a premium, to the extent that interest rate indexes exceed a specified rate, or “cap.” Floors are agreements whereby one party agrees to make payments to the other, in return for a premium, to the extent that interest rate indexes fall below a specified rate, or “floor.” The maximum potential amount of future payments that the Master Portfolio would be required to make under an interest rate cap would be the notional amount times the percentage increase in interest rates determined by the difference between the interest rate index current value and the value at the time the cap was entered into.

• Foreign currency options – The Master Portfolio may purchase and write foreign currency options, foreign currency futures and options on foreign currency futures to gain or reduce exposure to foreign currencies (foreign currency exchange rate risk). Foreign currency options give the purchaser the right to buy from or sell to the writer a foreign currency at any time before the expiration of the option.

• Barrier options – The Master Portfolio may purchase and write a variety of options with non-standard payout structures or other features (“barrier options”) that are generally traded OTC.

The Master Portfolio may invest in various types of barrier options, including down-and-out options, down-and-in options, double no-touch options, one-touch options, up-and-out options and up-and-in options. Down-and-out options expire worthless to the purchaser if the price of the underlying instrument falls below a specific barrier price level prior to the expiration date. Down-and-in options expire worthless to the purchaser unless the price of the underlying instrument falls below a specific barrier price level prior to the expiration date. Double no-touch options provide the purchaser an agreed-upon payout if the price of the underlying instrument does not reach or surpass predetermined barrier price levels prior to the option’s expiration date. One-touch options provide the purchaser an agreed-upon payout if the price of the underlying instrument reaches or surpasses predetermined barrier price levels prior to the expiration date. Up-and-out options expire worthless to the purchaser if the price of the underlying instrument increases beyond a predetermined barrier price level prior to the expiration date. Up-and-in options can only be exercised when the price of the underlying instrument increases beyond a predetermined barrier price level.

• Structured options – The Master Portfolio may invest in structured options to increase or decrease its exposure to an underlying index or group of securities (equity risk).

These options may consist of single or multiple OTC options which are priced as a single instrument. They may only be exercised at the expiration date, but may be transferred/sold prior to the expiration date. The value of a structured option may either increase or decrease with the underlying index or group of securities, depending on the combination of options used. Structured options are issued in units whereby each unit represents a structure based on the specific index with an initial reference strike price. One type of structure involves the combination of selling a put while buying a call on a specific index. This option would rise in value as the underlying index increases and fall in value as the underlying index decreases. Alternatively, another structure involves the sale of a call and the purchase of a put. This option structure would rise in value as the underlying index decreases and fall in value as the underlying index increases. Upon the exercise of the structured option, the Master Portfolio will receive a payment from, or be required to remit a payment to, the counterparty depending on the value of the underlying index at exercise.

In purchasing and writing options, the Master Portfolio bears the risk of an unfavorable change in the value of the underlying instrument or the risk that it may not be able to enter into a closing transaction due to an illiquid market. Exercise of a written option could result in the Master Portfolio purchasing or selling a security when it otherwise would not, or at a price different from the current market value.

NOTES   TO   FINANCIAL   STATEMENTS 109

Notes to Financial Statements (unaudited) (continued)

Swaps: Swap contracts are entered into to manage exposure to issuers, markets and securities. Such contracts are agreements between the Master Portfolio and a counterparty to make periodic net payments on a specified notional amount or a net payment upon termination. Swap agreements are privately negotiated in the OTC market and may be entered into as a bilateral contract (“OTC swaps”) or centrally cleared (“centrally cleared swaps”).

For OTC swaps, any upfront premiums paid and any upfront fees received are shown as swap premiums paid and swap premiums received, respectively, in the Statement of Assets and Liabilities and amortized over the term of the contract. The daily fluctuation in market value is recorded as unrealized appreciation (depreciation) on OTC Swaps in the Statement of Assets and Liabilities. Payments received or paid are recorded in the Statement of Operations as realized gains or losses, respectively. When an OTC swap is terminated, a realized gain or loss is recorded in the Statement of Operations equal to the difference between the proceeds from (or cost of) the closing transaction and the Master Portfolio’s basis in the contract, if any. Generally, the basis of the contract is the premium received or paid.

In a centrally cleared swap, immediately following execution of the swap contract, the swap contract is novated to a central counterparty (the “CCP”) and the CCP becomes the Master Portfolio’s counterparty on the swap. The Master Portfolio is required to interface with the CCP through the broker. Upon entering into a centrally cleared swap, the Master Portfolio is required to deposit initial margin with the broker in the form of cash or securities in an amount that varies depending on the size and risk profile of the particular swap. Securities deposited as initial margin are designated in the Schedule of Investments and cash deposited is shown as cash pledged for centrally cleared swaps in the Statement of Assets and Liabilities. Amounts pledged, which are considered restricted cash, are included in cash pledged for centrally cleared swaps in the Statement of Assets and Liabilities. Pursuant to the contract, the Master Portfolio agrees to receive from or pay to the broker variation margin. Variation margin is recorded as unrealized appreciation (depreciation) and shown as variation margin receivable (or payable) on centrally cleared swaps in the Statement of Assets and Liabilities. Payments received from (paid to) the counterparty are amortized over the term of the contract and recorded as realized gains (losses) in the Statement of Operations, including those at termination.

• Credit default swaps — Credit default swaps are entered into to manage exposure to the market or certain sectors of the market, to reduce risk exposure to defaults of corporate and/or sovereign issuers or to create exposure to corporate and/or sovereign issuers to which a fund is not otherwise exposed (credit risk).

The Master Portfolio may either buy or sell (write) credit default swaps on single-name issuers (corporate or sovereign), a combination or basket of single-name issuers or traded indexes. Credit default swaps are agreements in which the protection buyer pays fixed periodic payments to the seller in consideration for a promise from the protection seller to make a specific payment should a negative credit event take place with respect to the referenced entity (e.g., bankruptcy, failure to pay, obligation acceleration, repudiation, moratorium or restructuring). As a buyer, if an underlying credit event occurs, the Master Portfolio will either (i) receive from the seller an amount equal to the notional amount of the swap and deliver the referenced security or underlying securities comprising the index, or (ii) receive a net settlement of cash equal to the notional amount of the swap less the recovery value of the security or underlying securities comprising the index. As a seller (writer), if an underlying credit event occurs, the Master Portfolio will either pay the buyer an amount equal to the notional amount of the swap and take delivery of the referenced security or underlying securities comprising the index or pay a net settlement of cash equal to the notional amount of the swap less the recovery value of the security or underlying securities comprising the index.

• Total return swaps — Total return swaps are entered into to obtain exposure to a security or market without owning such security or investing directly in such market or to exchange the risk/return of one security or market (e.g., fixed-income) with another security or market (e.g., equity or commodity prices) (equity risk, commodity price risk and/or interest rate risk).

Total return swaps are agreements in which there is an exchange of cash flows whereby one party commits to make payments based on the total return (distributions plus capital gains/losses) of an underlying instrument, or basket of underlying instruments, in exchange for fixed or floating rate interest payments. If the total return of the instrument(s) or index underlying the transaction exceeds or falls short of the offsetting fixed or floating interest rate obligation, the Master Portfolio receives payment from or makes a payment to the counterparty.

Certain total return swaps are designed to function as a portfolio of direct investments in long and short equity positions. This means that the Master Portfolio has the ability to trade in and out of these long and short positions within the swap and will receive the economic benefits and risks equivalent to direct investment in these positions, subject to certain adjustments due to events related to the counterparty. Benefits and risks include capital appreciation (depreciation), corporate actions and dividends received and paid, all of which are reflected in the swap’s market value. The market value also includes interest charges and credits (“financing fees”) related to the notional values of the long and short positions and cash balances within the swap. These interest charges and credits are based on a specified benchmark rate plus or minus a specified spread determined based upon the country and/or currency of the positions in the Master Portfolio.

Positions within the swap and financing fees are reset periodically. During a reset, any unrealized appreciation (depreciation) on positions and accrued financing fees become available for cash settlement between the Master Portfolio and the counterparty. The amounts that are available for cash settlement are recorded as realized gains or losses in the Statement of Operations. Cash settlement in and out of the swap may occur at a reset date or any other date, at the discretion of the Master Portfolio and the counterparty, over the life of the agreement. Certain swaps have no stated expiration and can be terminated by either party at any time.

• Interest rate swaps — Interest rate swaps are entered into to gain or reduce exposure to interest rates or to manage duration, the yield curve or interest rate (interest rate risk).

Interest rate swaps are agreements in which one party pays a stream of interest payments, either fixed or floating, in exchange for another party’s stream of interest payments, either fixed or floating, on the same notional amount for a specified period of time. In more complex interest rate swaps, the notional principal amount may decline (or amortize) over time.

• Currency swaps — Currency swaps are entered into to gain or reduce exposure to foreign currencies (foreign currency exchange rate risk).

110 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Notes to Financial Statements (unaudited) (continued)

Currency swaps are interest rate swaps in which one party pays a stream of interest payments, either fixed or floating, in exchange for another party’s stream of interest payments, either fixed or floating, based on the notional amounts of two different currencies. The notional amounts are typically determined based on the spot exchange rates at the inception of the trade. Currency swaps may also involve an exchange of notional amounts at the start, during and/or at expiration of the contract, either at the current spot rate or another specified rate.

• Forward swaps — The Master Portfolio may enter into forward interest rate swaps and forward total return swaps. In a forward swap, the Master Portfolio and the counterparty agree to make periodic net payments beginning on a specified date or a net payment at termination.

• Inflation swaps — Inflation swaps are entered into to gain or reduce exposure to inflation (inflation risk). In an inflation swap, one party makes fixed interest payments on a notional principal amount in exchange for another party’s variable payments based on an inflation index, such as the Consumer Price Index.

Swap transactions involve, to varying degrees, elements of interest rate, credit and market risk in excess of the amounts recognized in the Statement of Assets and Liabilities. Such risks involve the possibility that there will be no liquid market for these agreements, that the counterparty to the agreements may default on its obligation to perform or disagree as to the meaning of the contractual terms in the agreements, and that there may be unfavorable changes in interest rates and/or market values associated with these transactions.

Master Netting Arrangements: In order to define its contractual rights and to secure rights that will help it mitigate its counterparty risk, the Master Portfolio may enter into an International Swaps and Derivatives Association, Inc. Master Agreement (“ISDA Master Agreement”) or similar agreement with its counterparties. An ISDA Master Agreement is a bilateral agreement between the Master Portfolio and a counterparty that governs certain OTC derivatives and typically contains, among other things, collateral posting terms and netting provisions in the event of a default and/or termination event. Under an ISDA Master Agreement, the Master Portfolio may, under certain circumstances, offset with the counterparty certain derivative financial instruments’ payables and/or receivables with collateral held and/or posted and create one single net payment. The provisions of the ISDA Master Agreement typically permit a single net payment in the event of default including the bankruptcy or insolvency of the counterparty. When the Master Portfolio enters into an ISDA Master Agreement and an MRA and/or MSLA with the same counterparty, the agreements may contain a set-off provision allowing the Master Portfolio to offset a net amount payable with amounts due to the Master Portfolio upon default of the counterparty. Bankruptcy or insolvency laws of a particular jurisdiction may restrict or prohibit the right of offset in bankruptcy, insolvency or other events. For example, notwithstanding what contractual rights may be included in an ISDA Master Agreement, such laws may prohibit the Master Portfolio from setting off amounts owed to a defaulting counterparty under an ISDA Master Agreement against amounts owed to the Master Portfolio by affiliates of the defaulting counterparty. The insolvency regimes of many jurisdictions do, however, generally permit set-off of simultaneous payables and receivables under certain types of financial contracts between the same legal entity upon a default of the entity, regardless of the existence of a contractual set-off right in those contracts.

Collateral Requirements: For derivatives traded under an ISDA Master Agreement, the collateral requirements are typically calculated by netting the mark-to-market amount for each transaction under such agreement and comparing that amount to the value of any collateral currently pledged by the Master Portfolio and the counterparty.

Cash collateral that has been pledged to cover obligations of the Master Portfolio and cash collateral received from the counterparty, if any, is reported separately in the Statement of Assets and Liabilities as cash pledged as collateral and cash received as collateral, respectively. Non-cash collateral pledged by the Master Portfolio, if any, is noted in the Schedule of Investments. Generally, the amount of collateral due from or to a counterparty is subject to a certain minimum transfer amount threshold before a transfer is required, which is determined at the close of business of the Master Portfolio. Any additional required collateral is delivered to/pledged by the Master Portfolio on the next business day. Typically, the counterparty is not permitted to sell, re-pledge or use cash and non-cash collateral it receives. The Master Portfolio generally agrees not to use non-cash collateral that it receives but may, absent default or certain other circumstances defined in the underlying ISDA Master Agreement, be permitted to use cash collateral received. In such cases, interest may be paid pursuant to the collateral arrangement with the counterparty. To the extent amounts due to the Master Portfolio from the counterparties are not fully collateralized, the Master Portfolio bears the risk of loss from counterparty non-performance. Likewise, to the extent the Master Portfolio has delivered collateral to a counterparty and stands ready to perform under the terms of its agreement with such counterparty, the Master Portfolio bears the risk of loss from a counterparty in the amount of the value of the collateral in the event the counterparty fails to return such collateral. Based on the terms of agreements, collateral may not be required for all derivative contracts.

For financial reporting purposes, the Master Portfolio does not offset derivative assets and derivative liabilities that are subject to netting arrangements, if any, in the Statement of Assets and Liabilities.

6. INVESTMENT ADVISORY AGREEMENT AND OTHER TRANSACTIONS WITH AFFILIATES

Investment Advisory: The Master Bond LLC, on behalf of the Master Portfolio, entered into an Investment Advisory Agreement with the Manager, the Master Portfolio’s investment adviser and an indirect, wholly-owned subsidiary of BlackRock, Inc. (“BlackRock”), to provide investment advisory and administrative services. The Manager is responsible for the management of the Master Portfolio’s portfolio and provides the personnel, facilities, equipment and certain other services necessary to the operations of the Master Portfolio.

For such services, the Master Portfolio pays the Manager a monthly fee at an annual rate equal to the following percentages of the average daily value of the Master Portfolio’s net assets:

Average Daily Net Assets	Investment Advisory Fees
First $250 million		0.16%
$250 million — $500 million		0.12
$500 million — $750 million		0.08
Greater than $750 million		0.05

NOTES   TO   FINANCIAL   STATEMENTS 111

Notes to Financial Statements (unaudited) (continued)

With respect to the Master Portfolio, the Manager entered into separate sub-advisory agreements with BlackRock International Limited (“BIL”) and BlackRock (Singapore) Limited (“BRS”), each an affiliate of the Manager. The Manager pays BIL and BRS for services they provide, for that portion of the Master Portfolio for which BIL and BRS, as applicable, act as sub-adviser, a monthly fee that is equal to a percentage of the investment advisory fees paid by the Master Portfolio to the Manager.

Expense Waivers and Reimbursements: With respect to the Master Portfolio, the Manager contractually agreed to waive its investment advisory fees by the amount of investment advisory fees the Master Portfolio pays to the Manager indirectly through its investment in affiliated money market funds (the “affiliated money market fund waiver”) through January 31, 2022. The contractual agreement may be terminated upon 90 days’ notice by a majority of the directors who are not “interested persons” of the Corporation, as defined in the 1940 Act (“Independent Directors”), or by a vote of a majority of the outstanding voting securities of the Master Portfolio. The amount of waivers and/or reimbursements of fees and expenses made pursuant to the expense limitation described below will be reduced by the amount of the affiliated money market fund waiver. Prior to January 28, 2020, this waiver was voluntary. This amount is included in fees waived and/or reimbursed by the Manager in the Statement of Operations. For the six months ended March 31, 2021 the amount waived was $207,286.

The Manager has contractually agreed to waive its investment advisory fee with respect to any portion of the Master Portfolio’s assets invested in affiliated equity and fixed-income mutual funds and affiliated exchange-traded funds that have a contractual management fee through January 31, 2022. The contractual agreement may be terminated upon 90 days’ notice by a majority of the Independent Directors, or by a vote of a majority of the outstanding voting securities of the Master Portfolio. This amount is included in fees waived and/or reimbursed by the Manager in the Statement of Operations. For the six months ended March 31, 2021, the Manager waived $41,687 in investment advisory fees pursuant to this arrangement.

For the six months ended March 31, 2021, the Master Bond LLC reimbursed the Manager $109,650 for certain accounting services, which is included in accounting services in the Statement of Operations.

Securities Lending: The U.S. Securities and Exchange Commission (“SEC”) has issued an exemptive order which permits BIM, an affiliate of the Manager, to serve as securities lending agent for the Master Portfolio, subject to applicable conditions. As securities lending agent, BIM bears all operational costs directly related to securities lending. The Master Portfolio is responsible for expenses in connection with the investment of cash collateral received for securities on loan (the “collateral investment expenses”). The cash collateral is invested in a private investment company, SL Liquidity Series, LLC, Money Market Series (the “Money Market Series”), managed by the Manager or its affiliates. However, BIM has agreed to cap the collateral investment expenses of the Money Market Series to an annual rate of 0.04%. The investment adviser to the Money Market Series will not charge any advisory fees with respect to shares purchased by the Master Portfolio. The Money Market Series may, under certain circumstances, impose a liquidity fee of up to 2% of the value withdrawn or temporarily restrict withdrawals for up to 10 business days during a 90 day period, in the event that the private investment company’s weekly liquid assets fall below certain thresholds. The Money Market Series seeks current income consistent with maintaining liquidity and preserving capital. Although the Money Market Series is not registered under the 1940 Act, its investments may follow the parameters of investments by a money market fund that is subject to Rule 2a-7 under the 1940 Act.

Securities lending income is equal to the total of income earned from the reinvestment of cash collateral, net of fees and other payments to and from borrowers of securities, and less the collateral investment expenses. The Master Portfolio retains a portion of securities lending income and remits a remaining portion to BIM as compensation for its services as securities lending agent.

Pursuant to the current securities lending agreement, the Master Portfolio retains 82% of securities lending income (which excludes collateral investment expenses), and this amount retained can never be less than 70% of the total of securities lending income plus the collateral investment expenses.

In addition, commencing the business day following the date that the aggregate securities lending income earned across the BlackRock Multi-Asset Complex in a calendar year exceeds a specified threshold, the Master Portfolio, pursuant to the securities lending agreement, will retain for the remainder of that calendar year securities lending income in an amount equal to 85% of securities lending income (which excludes collateral investment expenses), and this amount retained can never be less than 70% of the total of securities lending income plus the collateral investment expenses.

Prior to January 1, 2021, the Master Portfolio retained 75% of securities lending income (which excluded collateral investment expenses) and the amount retained could never be less than 70% of the total of securities lending income plus the collateral investment expenses. In addition, commencing the business day following the date that the aggregate securities lending income earned across the BlackRock Fixed-Income Complex in a calendar year exceeded a specified threshold, the Master Portfolio would retain for the remainder of that calendar year 85% of securities lending income (which excluded collateral investment expenses), and the amount retained could never be less than 70% of the total of securities lending income plus the collateral investment expenses.

The share of securities lending income earned by the Master Portfolio is shown as securities lending income — affiliated — net in the Statement of Operations. For the six months ended March 31, 2021, the Master Portfolio paid BIM $66,296 for securities lending agent services.

Interfund Lending: In accordance with an exemptive order (the “Order”) from the SEC, the Master Portfolio may participate in a joint lending and borrowing facility for temporary purposes (the “Interfund Lending Program”), subject to compliance with the terms and conditions of the Order, and to the extent permitted by the Master Portfolio’s investment policies and restrictions. The Master Portfolio is currently permitted to borrow under the Interfund Lending Program.

A lending BlackRock fund may lend in aggregate up to 15% of its net assets, but may not lend more than 5% of its net assets to any one borrowing fund through the Interfund Lending Program. A borrowing BlackRock fund may not borrow through the Interfund Lending Program or from any other source more than 33 1/3% of its total assets (or any lower threshold provided for by the fund’s investment restrictions). If a borrowing BlackRock fund’s total outstanding borrowings exceed 10% of its total assets, each of its outstanding interfund loans will be subject to collateralization of at least 102% of the outstanding principal value of the loan. All interfund loans are for temporary or emergency purposes and the interest rate to be charged will be the average of the highest current overnight repurchase agreement rate available to a lending fund and the bank loan rate, as calculated according to a formula established by the Board.

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Notes to Financial Statements (unaudited) (continued)

During the six months ended March 31, 2021, the Master Portfolio did not participate in the Interfund Lending Program.

Directors and Officers: Certain directors and/or officers of the Master Bond LLC are directors and/or officers of BlackRock or its affiliates.

Other Transactions: The Master Portfolio may purchase securities from, or sell securities to, an affiliated fund provided the affiliation is due solely to having a common investment adviser, common officers, or common directors. For the six months ended March 31, 2021, the purchase and sale transactions and any net realized gains (losses) with an affiliated fund in compliance with Rule 17a-7 under the 1940 Act were as follows:

Purchases	Sales		Net Realized Gain
$ 8,115,182	$	8,532,668	$   67,875

7. PURCHASES AND SALES

For the six months ended March 31, 2021, purchases and sales of investments, including paydowns and mortgage dollar rolls and excluding short-term investments transactions, were as follows:

	Purchases		Sales
Non-U.S. Government Securities	$	47,978,060,446	$	47,751,792,009
U.S. Government Securities		1,513,911,575		1,946,498,037

For the six months ended March 31, 2021, purchases and sales related to mortgage dollar rolls were as follows:

	Purchases		Sales
Mortgage Dollar Rolls	$	31,749,005,770	$	31,747,118,062

8. INCOME TAX INFORMATION

It is the Master Portfolio’s policy to comply with the requirements of the Internal Revenue Code of 1986, as amended, applicable to regulated investment companies, and to distribute substantially all of its taxable income to its shareholders. Therefore, no U.S. federal income tax provision is required.

The Master Portfolio is classified as a partnership for U.S. federal income tax purposes. As such, each investor in the Master Portfolio is treated as the owner of its proportionate share of net assets, income, expenses and realized and unrealized gains and losses of the Master Portfolio. Therefore, no U.S. federal income tax provision is required. It is intended that the Master Portfolio’s assets will be managed so an investor in the Master Portfolio can satisfy the requirements of Subchapter M of the Internal Revenue Code of 1986, as amended.

The Master Portfolio files U.S. federal and various state and local tax returns. No income tax returns are currently under examination. The statute of limitations on the Master Portfolio’s U.S. federal tax returns generally remains open for a period of three fiscal years after they are filed. The statutes of limitations on the Master Portfolio’s state and local tax returns may remain open for an additional year depending upon the jurisdiction.

Management has analyzed tax laws and regulations and their application to the Master Portfolio as of March 31, 2021, inclusive of the open tax return years, and does not believe that there are any uncertain tax positions that require recognition of a tax liability in the Master Portfolio’s financial statements.

As of March 31, 2021, gross unrealized appreciation and depreciation based on cost of investments (including short positions and derivatives, if any) for U.S. federal income tax purposes were as follows:

		Amounts
Tax cost	$	30,405,634,015
Gross unrealized appreciation	$	676,534,138
Gross unrealized depreciation		(586,469,061	)
Net unrealized appreciation (depreciation)	$	90,065,077

9. BANK BORROWINGS

The Master Bond LLC, on behalf of the Master Portfolio, along with certain other funds managed by the Manager and its affiliates (“Participating Funds”), is a party to a 364-day, $2.25 billion credit agreement with a group of lenders. Under this agreement, the Master Portfolio may borrow to fund shareholder redemptions. Excluding commitments designated for certain individual funds, the Participating Funds, including the Master Portfolio, can borrow up to an aggregate commitment amount of $1.75 billion at any time outstanding, subject to asset coverage and other limitations as specified in the agreement. The credit agreement has the following terms: a fee of 0.10% per annum on unused commitment amounts and interest at a rate equal to the higher of (a) one-month LIBOR (but, in any event, not less than 0.00%) on the date the loan is made plus 0.80% per annum or (b) the Fed Funds rate (but, in any event, not less than 0.00%) in effect from time to time plus 0.80% per annum on amounts borrowed. The agreement expires in April 2021 unless extended or renewed. These fees were allocated among such funds based upon portions of the aggregate commitment available to them and relative net assets of Participating Funds. During the six months ended March 31, 2021, the Master Portfolio did not borrow under the credit agreement.

NOTES   TO   FINANCIAL   STATEMENTS 113

Notes to Financial Statements (unaudited) (continued)

10. PRINCIPAL RISKS

In the normal course of business, the Master Portfolio invests in securities or other instruments and may enter into certain transactions, and such activities subject the Master Portfolio to various risks, including among others, fluctuations in the market (market risk) or failure of an issuer to meet all of its obligations. The value of securities or other instruments may also be affected by various factors, including, without limitation: (i) the general economy; (ii) the overall market as well as local, regional or global political and/or social instability; (iii) regulation, taxation or international tax treaties between various countries; or (iv) currency, interest rate and price fluctuations. Local, regional or global events such as war, acts of terrorism, the spread of infectious illness or other public health issues, recessions, or other events could have a significant impact on the Master Portfolio and its investments. The Master Portfolio’s prospectus provides details of the risks to which the Master Portfolio is subject.

The Master Portfolio may be exposed to additional risks when reinvesting cash collateral in money market funds that do not seek to maintain a stable NAV per share of $1.00, which may be subject to redemption gates or liquidity fees under certain circumstances.

Market Risk: The Master Portfolio may be exposed to prepayment risk, which is the risk that borrowers may exercise their option to prepay principal earlier than scheduled during periods of declining interest rates, which would force the Master Portfolio to reinvest in lower yielding securities. The Master Portfolio may also be exposed to reinvestment risk, which is the risk that income from the Master Portfolio’s portfolio will decline if the Master Portfolio invests the proceeds from matured, traded or called fixed-income securities at market interest rates that are below the Master Portfolio’s current earnings rate.

Municipal securities are subject to the risk that litigation, legislation or other political events, local business or economic conditions, credit rating downgrades, or the bankruptcy of the issuer could have a significant effect on an issuer’s ability to make payments of principal and/or interest or otherwise affect the value of such securities. Municipal securities can be significantly affected by political or economic changes, including changes made in the law after issuance of the securities, as well as uncertainties in the municipal market related to, taxation, legislative changes or the rights of municipal security holders, including in connection with an issuer insolvency. Municipal securities backed by current or anticipated revenues from a specific project or specific assets can be negatively affected by the discontinuance of the tax benefits supporting the project or assets or the inability to collect revenues for the project or from the assets. Municipal securities may be less liquid than taxable bonds, and there may be less publicly available information on the financial condition of municipal security issuers than for issuers of other securities.

An outbreak of respiratory disease caused by a novel coronavirus has developed into a global pandemic and has resulted in closing borders, quarantines, disruptions to supply chains and customer activity, as well as general concern and uncertainty. The impact of this pandemic, and other global health crises that may arise in the future, could affect the economies of many nations, individual companies and the market in general in ways that cannot necessarily be foreseen at the present time. This pandemic may result in substantial market volatility and may adversely impact the prices and liquidity of a fund’s investments. The duration of this pandemic and its effects cannot be determined with certainty.

Valuation Risk: The market values of equities, such as common stocks and preferred securities or equity related investments, such as futures and options, may decline due to general market conditions which are not specifically related to a particular company. They may also decline due to factors which affect a particular industry or industries. The Master Portfolio may invest in illiquid investments. An illiquid investment is any investment that the Master Portfolio reasonably expects cannot be sold or disposed of in current market conditions in seven calendar days or less without the sale or disposition significantly changing the market value of the investment. The Master Portfolio may experience difficulty in selling illiquid investments in a timely manner at the price that it believes the investments are worth. Prices may fluctuate widely over short or extended periods in response to company, market or economic news. Markets also tend to move in cycles, with periods of rising and falling prices. This volatility may cause the Master Portfolio’s NAV to experience significant increases or decreases over short periods of time. If there is a general decline in the securities and other markets, the NAV of the Master Portfolio may lose value, regardless of the individual results of the securities and other instruments in which the Master Portfolio invests.

The price the Master Portfolio could receive upon the sale of any particular portfolio investment may differ from the Master Portfolio’s valuation of the investment, particularly for securities that trade in thin or volatile markets or that are valued using a fair valuation technique or a price provided by an independent pricing service. Changes to significant unobservable inputs and assumptions (i.e., publicly traded company multiples, growth rate, time to exit) due to the lack of observable inputs may significantly impact the resulting fair value and therefore the Master Portfolio’s results of operations. As a result, the price received upon the sale of an investment may be less than the value ascribed by the Master Portfolio, and the Master Portfolio could realize a greater than expected loss or lesser than expected gain upon the sale of the investment. The Master Portfolio’s ability to value its investments may also be impacted by technological issues and/or errors by pricing services or other third party service providers.

Counterparty Credit Risk: The Master Portfolio may be exposed to counterparty credit risk, or the risk that an entity may fail to or be unable to perform on its commitments related to unsettled or open transactions, including making timely interest and/or principal payments or otherwise honoring its obligations. The Master Portfolio manages counterparty credit risk by entering into transactions only with counterparties that the Manager believes have the financial resources to honor their obligations and by monitoring the financial stability of those counterparties. Financial assets, which potentially expose the Master Portfolio to market, issuer and counterparty credit risks, consist principally of financial instruments and receivables due from counterparties. The extent of the Master Portfolio’s exposure to market, issuer and counterparty credit risks with respect to these financial assets is approximately their value recorded in the Statement of Assets and Liabilities, less any collateral held by the Master Portfolio.

A derivative contract may suffer a mark-to-market loss if the value of the contract decreases due to an unfavorable change in the market rates or values of the underlying instrument. Losses can also occur if the counterparty does not perform under the contract.

For OTC options purchased, the Master Portfolio bears the risk of loss in the amount of the premiums paid plus the positive change in market values net of any collateral held by the Master Portfolio should the counterparty fail to perform under the contracts. Options written by the Master Portfolio do not typically give rise to counterparty credit risk, as options written generally obligate the Master Portfolio, and not the counterparty, to perform. The Master Portfolio may be exposed to counterparty credit risk with respect to options written to the extent the Master Portfolio deposits collateral with its counterparty to a written option.

With exchange-traded options purchased and exchange-traded futures and centrally cleared swaps, there is less counterparty credit risk to the Master Portfolio since the exchange or clearinghouse, as counterparty to such instruments, guarantees against a possible default. The clearinghouse stands between the buyer and the seller of the

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Notes to Financial Statements (unaudited) (continued)

contract; therefore, credit risk is limited to failure of the clearinghouse. While offset rights may exist under applicable law, the Master Portfolio does not have a contractual right of offset against a clearing broker or clearinghouse in the event of a default (including the bankruptcy or insolvency). Additionally, credit risk exists in exchange-traded futures and centrally cleared swaps with respect to initial and variation margin that is held in a clearing broker’s customer accounts. While clearing brokers are required to segregate customer margin from their own assets, in the event that a clearing broker becomes insolvent or goes into bankruptcy and at that time there is a shortfall in the aggregate amount of margin held by the clearing broker for all its clients, typically the shortfall would be allocated on a pro rata basis across all the clearing broker’s customers, potentially resulting in losses to the Master Portfolio.

Concentration Risk: A diversified portfolio, where this is appropriate and consistent with the Master Portfolio’s objectives, minimizes the risk that a price change of a particular investment will have a material impact on the NAV of the Master Portfolio. The investment concentrations within the Master Portfolio’s portfolio are disclosed in its Schedule of Investments.

The Master Portfolio invests a significant portion of its assets in fixed-income securities and/or uses derivatives tied to the fixed-income markets. Changes in market interest rates or economic conditions may affect the value and/or liquidity of such investments. Interest rate risk is the risk that prices of bonds and other fixed-income securities will increase as interest rates fall and decrease as interest rates rise. The Master Portfolio may be subject to a greater risk of rising interest rates due to the current period of historically low rates.

The Master Portfolio invests a significant portion of its assets in securities backed by commercial or residential mortgage loans or in issuers that hold mortgage and other asset-backed securities. When the Master Portfolio concentrates its investments in this manner, it assumes a greater risk of prepayment or payment extension by securities issuers. Changes in economic conditions, including delinquencies and/or defaults on assets underlying these securities, can affect the value, income and/or liquidity of such positions. Investment percentages in these securities are presented in the Schedule of Investments.

LIBOR Transition Risk: The United Kingdom’s Financial Conduct Authority announced a phase out of the London Interbank Offered Rate (“LIBOR”). Although many LIBOR rates will be phased out by the end of 2021, a selection of widely used USD LIBOR rates will continue to be published through June 2023 in order to assist with the transition. The Master Portfolio may be exposed to financial instruments tied to LIBOR to determine payment obligations, financing terms, hedging strategies or investment value. The transition process away from LIBOR might lead to increased volatility and illiquidity in markets for, and reduce the effectiveness of new hedges placed against, instruments whose terms currently include LIBOR. The ultimate effect of the LIBOR transition process on the Master Portfolio is uncertain.

11. SUBSEQUENT EVENTS

Management’s evaluation of the impact of all subsequent events on the Master Portfolio’s financial statements was completed through the date the financial statements were issued and the following item was noted:

Effective April 15, 2021, the credit agreement was extended until April 2022 under substantially the same terms.

NOTES   TO   FINANCIAL   STATEMENTS 115

Statement Regarding Liquidity Risk Management Program

In compliance with Rule 22e-4 under the Investment Company Act of 1940, as amended (the “Liquidity Rule”), BlackRock Bond Fund, Inc. (the “Corporation”) has adopted and implemented a liquidity risk management program (the “Program”) for BlackRock Total Return Fund, and Master Bond LLC, on behalf of Master Total Return Portfolio, which is reasonably designed to assess and manage the Fund’s liquidity risk.

The Board of Directors (the “Board”) of the Corporation, on behalf of the Master Bond LLC, met on November 10-11, 2020 (the “Meeting”) to review the Program. The Board previously appointed BlackRock Advisors, LLC or BlackRock Fund Advisors (“BlackRock���), each an investment adviser to certain funds, as the program administrator for each Fund’s Program, as applicable. BlackRock also previously delegated oversight of the Program to the 40 Act Liquidity Risk Management Committee (the “Committee”). At the Meeting, the Committee, on behalf of BlackRock, provided the Board with a report that addressed the operation of the Program and assessed its adequacy and effectiveness of implementation, including the management of each Fund’s Highly Liquid Investment Minimum (“HLIM”) where applicable, and any material changes to the Program (the “Report”). The Report covered the period from October 1, 2019 through September 30, 2020 (the “Program Reporting Period”).

The Report described the Program’s liquidity classification methodology for categorizing a Fund’s investments (including derivative transactions) into one of four liquidity buckets. It also referenced the methodology used by BlackRock to establish a Fund’s HLIM and noted that the Committee reviews and ratifies the HLIM assigned to each Fund no less frequently than annually. The Report also discussed notable events affecting liquidity over the Program Reporting Period, including the impact of the coronavirus outbreak on the Funds and the overall market.

The Report noted that the Program complied with the key factors for consideration under the Liquidity Rule for assessing, managing and periodically reviewing a Fund’s liquidity risk, as follows:

a) The Fund’s investment strategy and liquidity of portfolio investments during both normal and reasonably foreseeable stressed conditions. During the Program Reporting Period, the Committee reviewed whether each Fund’s strategy is appropriate for an open-end fund structure with a focus on Funds with more significant and consistent holdings of less liquid and illiquid assets. The Committee also factored a Fund’s concentration in an issuer into the liquidity classification methodology by taking issuer position sizes into account. Where a Fund participated in borrowings for investment purposes (such as tender option bonds and reverse repurchase agreements), such borrowings were factored into the Program’s calculation of a Fund’s liquidity bucketing. Derivative exposure was also considered in such calculation.

b) Short-term and long-term cash flow projections during both normal and reasonably foreseeable stressed conditions. During the Program Reporting Period, the Committee reviewed historical net redemption activity and used this information as a component to establish each Fund’s reasonably anticipated trading size (“RATS”). Each Fund has adopted an in-kind redemption policy which may be utilized to meet larger redemption requests. The Committee may also take into consideration a Fund’s shareholder ownership concentration (which, depending on product type and distribution channel, may or may not be available), a Fund’s distribution channels, and the degree of certainty associated with a Fund’s short-term and long-term cash flow projections.

c) Holdings of cash and cash equivalents, as well as borrowing arrangements. The Committee considered the terms of the credit facility committed to the Funds, the financial health of the institution providing the facility and the fact that the credit facility is shared among multiple Funds (including that a portion of the aggregate commitment amount is specifically designated for BlackRock Floating Rate Income Portfolio, a series of BlackRock Funds V). The Committee also considered other types of borrowing available to the Funds, such as the ability to use reverse repurchase agreements and interfund lending, as applicable.

There were no material changes to the Program during the Program Reporting Period. The Report provided to the Board stated that the Committee concluded that based on the operation of the functions, as described in the Report, the Program is operating as intended and is effective in implementing the requirements of the Liquidity Rule.

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Additional Information  

Regulation Regarding Derivatives

On October 28, 2020, the Securities and Exchange Commission (the “SEC”) adopted new regulations governing the use of derivatives by registered investment companies (“Rule 18f-4”). The Master Bond LLC will be required to implement and comply with Rule 18f-4 by August 19, 2022. Once implemented, Rule 18f-4 will impose limits on the amount of derivatives a fund can enter into, eliminate the asset segregation framework currently used by funds to comply with Section 18 of the 1940 Act, treat derivatives as senior securities and require funds whose use of derivatives is more than a limited specified exposure amount to establish and maintain a comprehensive derivatives risk management program and appoint a derivatives risk manager.

General Information

Householding

The Fund will mail only one copy of shareholder documents, including prospectuses, annual and semi-annual reports and proxy statements, to shareholders with multiple accounts at the same address. This practice is commonly called “householding” and is intended to reduce expenses and eliminate duplicate mailings of shareholder documents. Mailings of your shareholder documents may be householded indefinitely unless you instruct us otherwise. If you do not want the mailing of these documents to be combined with those for other members of your household, please call the Fund at (800) 441-7762.

Availability of Quarterly Schedule of Investments

The Fund/Master Bond LLC file their complete schedule of portfolio holdings with the SEC for the first and third quarters of each fiscal year as an exhibit to their reports on Form N-PORT. The Fund’s/Master Bond LLC’s Forms N-PORT are available on the SEC’s website at sec.gov. Additionally, the Fund/Master Bond LLC make their portfolio holdings for the first and third quarters of each fiscal year available at blackrock.com/fundreports.

Availability of Proxy Voting Policies, Procedures and Voting Records

A description of the policies and procedures that the Fund/Master Bond LLC use to determine how to vote proxies relating to portfolio securities and information about how the Fund/Master Bond LLC voted proxies relating to securities held in the Fund’s/Master Bond LLC’s portfolios during the most recent 12-month period ended June 30 is available without charge, upon request (1) by calling (800) 441-7762; (2) on the BlackRock website at blackrock.com; and (3) on the SEC’s website at sec.gov.

BlackRock’s Mutual Fund Family

BlackRock offers a diverse lineup of open-end mutual funds crossing all investment styles and managed by experts in equity, fixed-income and tax-exempt investing. Visit blackrock.com for more information.

Shareholder Privileges

Account Information

Call us at (800) 441-7762 from 8:00 AM to 6:00 PM ET on any business day to get information about your account balances, recent transactions and share prices. You can also visit blackrock.com for more information.

Automatic Investment Plans

Investor class shareholders who want to invest regularly can arrange to have $50 or more automatically deducted from their checking or savings account and invested in any of the BlackRock funds.

Systematic Withdrawal Plans

Investor class shareholders can establish a systematic withdrawal plan and receive periodic payments of $50 or more from their BlackRock funds, as long as their account balance is at least $10,000.

Retirement Plans

Shareholders may make investments in conjunction with Traditional, Rollover, Roth, Coverdell, Simple IRAs, SEP IRAs and 403(b) Plans.

ADDITIONAL  INFORMATION 117

Additional Information  (continued)

BlackRock Privacy Principles

BlackRock is committed to maintaining the privacy of its current and former fund investors and individual clients (collectively, “Clients”) and to safeguarding their non-public personal information. The following information is provided to help you understand what personal information BlackRock collects, how we protect that information and why in certain cases we share such information with select parties.

If you are located in a jurisdiction where specific laws, rules or regulations require BlackRock to provide you with additional or different privacy-related rights beyond what is set forth below, then BlackRock will comply with those specific laws, rules or regulations.

BlackRock obtains or verifies personal non-public information from and about you from different sources, including the following: (i) information we receive from you or, if applicable, your financial intermediary, on applications, forms or other documents; (ii) information about your transactions with us, our affiliates, or others; (iii) information we receive from a consumer reporting agency; and (iv) from visits to our websites.

BlackRock does not sell or disclose to non-affiliated third parties any non-public personal information about its Clients, except as permitted by law or as is necessary to respond to regulatory requests or to service Client accounts. These non-affiliated third parties are required to protect the confidentiality and security of this information and to use it only for its intended purpose.

We may share information with our affiliates to service your account or to provide you with information about other BlackRock products or services that may be of interest to you. In addition, BlackRock restricts access to non-public personal information about its Clients to those BlackRock employees with a legitimate business need for the information. BlackRock maintains physical, electronic and procedural safeguards that are designed to protect the non-public personal information of its Clients, including procedures relating to the proper storage and disposal of such information.

Fund and/or Master Bond LLC Service Providers

Investment Adviser

BlackRock Advisors, LLC

Wilmington, DE 19809

Sub-Advisers

BlackRock International Limited

Edinburgh, EH3 8BL

United Kingdom

BlackRock (Singapore) Limited

079912 Singapore

Accounting Agent and Transfer Agent

BNY Mellon Investment Servicing (US) Inc.

Wilmington, DE 19809

Custodian

The Bank of New York Mellon

New York, NY 10286

Independent Registered Public Accounting Firm

Deloitte & Touche LLP

Boston, MA 19103

Distributor

BlackRock Investments, LLC

New York, NY 10022

Legal Counsel

Willkie Farr & Gallagher LLP

New York, NY 10019

Address of the Corporation/Master Bond LLC

100 Bellevue Parkway

Wilmington, DE 19809

118 2 0 2 1   BLACK ROCK   SEMI - ANNUAL   REPORT   TO   SHAREHOLDERS

Glossary of Terms Used in this Report  

Currency Abbreviation
AUD	Australian Dollar
BRL	Brazilian Real
CAD	Canadian Dollar
CLP	Chilean Peso
CNH	Chinese Yuan Offshore
CNY	Chinese Yuan
COP	Colombian Peso
EUR	Euro
GBP	British Pound
HKD	Hong Kong Dollar
HUF	Hungarian Forint
IDR	Indonesian Rupiah
INR	Indian Rupee
JPY	Japanese Yen
KZT	Kazakhstani Tenge
MXN	Mexican Peso
PLN	Polish Zloty
RUB	Russian Ruble
SGD	Singapore Dollar
TRY	Turkish Lira
USD	United States Dollar
ZAR	South African Rand

Portfolio Abbreviation
ABS	Asset-Backed Security
AKA	Also Known As
CD	Certificate of Deposit
CDO	Collateralized Debt Obligation
CLICP	Chile Indice de Camara Promedio Interbank Overnight Index
CLN	Credit-Linked-Note
CLO	Collateralized Loan Obligation
CORRA	Canadian OvernightRepo Rate Average
DAC	Designated Activity Co.
ETF	Exchange-Traded Fund
EURIBOR	Euro Interbank Offered Rate
FKA	Formally Known As
GMTN	Global Medium-Term Note
GO	General Obligation Bonds
HFA	Housing Finance Agency
IO	Interest Only
LIBOR	London Interbank Offered Rate
LP	Limited Partnership
MTN	Medium-Term Note
MXIBTIIE	Mexico Interbank TIIE 28-Day
OTC	Over-the-Counter
PIK	Payment-in-Kind
RB	Revenue Bonds
REMIC	Real Estate Mortgage Investment Conduit
S&P	Standard & Poor’s
SONIA	Sterling Overnight Index Average
SPDR	Standard & Poor’s Depository Receipt
TBA	To-be-Announced
UK RPI	United Kingdom Retail Price Index

GLOSSARY  OF  TERMS  USED  IN  THIS  REPORT 119

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This report is intended for current holders. It is not authorized for use as an offer of sale or a solicitation of an offer to buy shares of the Fund unless preceded or accompanied by the Fund’s current prospectus. Past performance results shown in this report should not be considered a representation of future performance. Investment returns and principal value of shares will fluctuate so that shares, when redeemed, may be worth more or less than their original cost. Statements and other information herein are as dated and are subject to change.

TR-3/21-SAR

(b) Not Applicable

Item 2 – Code of Ethics – Not Applicable to this semi-annual report

Item 3 – Audit Committee Financial Expert – Not Applicable to this semi-annual report

Item 4 – Principal Accountant Fees and Services – Not Applicable to this semi-annual report

Item 5 – Audit Committee of Listed Registrants – Not Applicable

Item 6 – Investments

(a) The registrants’ Schedules of Investments are included as part of the Report to Stockholders filed under Item 1 of this Form.

(b) Not Applicable due to no such divestments during the semi-annual period covered since the previous Form N-CSR filing.

Item 7 – Disclosure of Proxy Voting Policies and Procedures for Closed-End Management Investment Companies – Not Applicable

Item 8 – Portfolio Managers of Closed-End Management Investment Companies – Not Applicable

Item 9 – Purchases of Equity Securities by Closed-End Management Investment Company and Affiliated Purchasers – Not Applicable

Item 10 – Submission of Matters to a Vote of Security Holders – There have been no material changes to these procedures.

Item 11 – Controls and Procedures

(a) The registrants’ principal executive and principal financial officers, or persons performing similar functions, have concluded that the registrants’ disclosure controls and procedures (as defined in Rule 30a-3(c) under the Investment Company Act of 1940, as amended (the “1940 Act”)) are effective as of a date within 90 days of the filing of this report based on the evaluation of these controls and procedures required by Rule 30a-3(b) under the 1940 Act and Rule 15d-15(b) under the Securities Exchange Act of 1934, as amended.

(b) There were no changes in the registrants’ internal control over financial reporting (as defined in Rule 30a-3(d) under the 1940 Act) that occurred during the period covered by this report that have materially affected, or are reasonably likely to materially affect, the registrants’ internal control over financial reporting.

Item 12 – Disclosure of Securities Lending Activities for Closed-End Management Investment

Companies – Not Applicable

Item 13 – Exhibits attached hereto

(a)(1) Code of Ethics – Not Applicable to this semi-annual report

(a)(2) Section 302 Certifications are attached

(a)(3) Not Applicable

(a)(4) Not Applicable

(b) Section 906 Certifications are attached

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, each registrant has duly caused this report to be signed on its behalf by the undersigned, thereunto duly authorized.

BlackRock Total Return Fund of BlackRock Bond Fund, Inc. and Master Total Return Portfolio of Master Bond LLC

By:	/s/ John M. Perlowski
	John M. Perlowski
	Chief Executive Officer (principal executive officer) of
	BlackRock Total Return Fund of BlackRock Bond Fund, Inc. and Master Total Return Portfolio of Master Bond LLC

Date: June 3, 2021

Pursuant to the requirements of the Securities Exchange Act of 1934 and the Investment Company Act of 1940, this report has been signed below by the following persons on behalf of each registrant and in the capacities and on the dates indicated.

By:	/s/ John M. Perlowski
	John M. Perlowski
	Chief Executive Officer (principal executive officer) of
	BlackRock Total Return Fund of BlackRock Bond Fund, Inc. and Master Total Return Portfolio of Master Bond LLC

Date: June 3, 2021

By:	/s/ Trent Walker
	Trent Walker
	Chief Financial Officer (principal financial officer) of
	BlackRock Total Return Fund of BlackRock Bond Fund, Inc. and Master Total Return Portfolio of Master Bond LLC

Date: June 3, 2021