[Janus letterhead]

February 17, 2010

VIA EDGAR

Mr. Larry Greene
Division of Investment Management
U.S. Securities and Exchange Commission
100 F Street, N.E.
Washington, DC 20549-0505

Re: JANUS INVESTMENT FUND (the "Registrant")
    1933 Act File No. 002-34393
    1940 Act File No. 811-01879
    Post-Effective Amendment No. 127

Dear Mr. Greene:

On behalf of the Registrant and its funds or portfolios (each, a "Fund" and
collectively, the "Funds"), this letter is to respond to your comments made by
telephone on January 21, 2010 with respect to the Registrant's Post-Effective
Amendment No. 127 filed pursuant to Rule 485(a) under the Securities Act of
1933, as amended, on November 24, 2009. The Staff of the Securities and Exchange
Commission's (the "Staff") comments and the Registrant's responses to Staff
comments are as follows:

     1.   COMMENT: The Staff requested that the Registrant reflect in writing
          all comments and responses and carry over comments, as applicable, to
          the Registrant's other Prospectuses and Statements of Additional
          Information ("SAIs").

          RESPONSE: The Registrant acknowledges the comment and confirms that it
          has complied.

Prospectus Comments

     2.   COMMENT: With respect to the Funds, the Staff noted that for Funds
          with global, international or worldwide in their names, such Funds
          should each invest in securities of at least ten countries and invest
          at least 40% of their respective assets in securities of foreign
          countries, excluding the U.S.

          RESPONSE: Consistent with investment policies and restrictions of
          these Funds, the Registrant has previously added or revised disclosure
          as appropriate to reflect that such Funds invest in several countries.
          The Registrant believes these investment policies are consistent with
          formal SEC guidance.

     3.   COMMENT: Where a Fund has an expense reimbursement or fee waiver
          arrangement that reduces Fund Operating Expenses, the Staff requested
          that Registrant amend its Fees and Expenses tables to include the
          caption "Net Total Operating Expenses" below the "Fee Waiver" caption
          showing the Fund's operating expenses waived. The Staff indicated that
          a Fund should not use the caption "Total Operating Expenses" twice in
          the Fees and Expenses table.



          RESPONSE: The Registrant acknowledges the comment and has updated the
          disclosure as requested. However, the Registrant notes that
          Instruction 3(e) to Item 3 of Form N-1A states that a Fund should use
          appropriate descriptive captions, such as "Fee Waiver [and/or Expense
          Reimbursement]" and "Total Annual Fund Operating Expenses After Fee
          Waiver [and/or Expense Reimbursement]" when it has expense
          reimbursement or fee waiver arrangements that will reduce any Fund
          operating expenses. The Registrant believes that its use of "Total
          Operating Expenses After Fee Waiver" complied with Form N-1A
          instructions.

     4.   COMMENT: With regards to the Fees and Expenses table in the Summary
          Section of the Prospectus, the Staff indicated that a footnote to the
          table pertaining to a Fund's performance adjusted management fee is
          not permitted under Form N-1A. The Staff suggested that the Registrant
          note in parentheses next to "Management Fee" in the table that the
          management fee is subject to a performance fee.

          RESPONSE: The Registrant has updated its Fees and Expenses table to
          include the phrase "may adjust up or down" in parentheses next to
          "Management Fee" in the table. The footnote explaining the Fund's
          performance fee has been deleted. While the Registrant has amended its
          Fees and Expenses table per the Staff's request, the Registrant
          strongly believes that a footnote explaining the Fund's use of
          performance-based management fees is appropriate and should be
          permitted given the unique nature of these types of fees.

     5.   COMMENT: The Staff indicated that the narrative before the Fees and
          Expenses Example should be amended to delete the sentence "It also
          shows costs if you sold your Shares at the end of the period or
          continued to hold them." The Staff noted that Item 3 of Form N-1A does
          not allow this disclosure.

          RESPONSE: The Registrant acknowledges the comment and has updated the
          disclosure as appropriate.

     6.   COMMENT: The Staff indicated that the table in the Fees and Expenses
          Example should contain two separate tables that provide expense
          examples if shares were held and sold. The Staff requested that the
          Registrant follow the example provided in Item 3 of Form N-1A.

          RESPONSE: The Registrant acknowledges the comment and has updated the
          disclosure as appropriate.

     7.   COMMENT: With regards to the Annual Total Return table in the Summary
          Section of the Prospectus, the Staff requested that the Registrant
          confirm that footnotes regarding a contingent deferred sales charge,
          "Return After Taxes on Distributions and Sale of Fund Shares," and
          "Before Tax Returns" are permitted as disclosed under Form N-1A. In
          addition, the Staff noted that a description of a broad-based index
          used in the table is not permitted under Form N-1A and further
          requested that Registrant confirm such description is permissible
          under Form N-1A.

          RESPONSE: The Registrant believes that the disclosures relating to a
          contingent deferred sales charge, "Return After Taxes on Distributions
          and Sale of Fund Shares," and "Before Tax Returns" are permitted under
          Item 4(b)(2)(iv) of Form N-1A. The Registrant acknowledges the Staff's
          comment regarding index descriptions and has updated the disclosure as
          appropriate.



     8.   COMMENT: With regards to "Purchase and Sale of Fund Shares" in the
          Summary Section of the Prospectus, the Staff indicated that references
          to financial intermediary transaction processing fees and requests
          received in "good order" are not permitted by Item 6 of Form N-1A. The
          Staff stated that only disclosure about a Fund's minimum initial or
          subsequent investment requirements and procedures for redeeming shares
          is permitted under Form N-1A.

          RESPONSE: The Registrant acknowledges the Staff's comments and has
          deleted references to financial intermediary transaction processing
          fees. However, the Registrant strongly believes that the Fund's
          description of the receipt of purchase, exchange and redemption
          request in "good order" from financial intermediaries is allowed under
          Item 6 of Form N-1A. Item 6 states that the Fund should describe
          investment requirements and redemption procedures. A purchase,
          exchange or redemption request cannot be processed by the Fund unless
          a financial intermediary delivers a request in "good order" and
          complies with this procedure. The Registrant believes that this
          disclosure complies with the instructions in Form N-1A and has
          retained its disclosure.

     9.   COMMENT: With respect to Janus Global Life Sciences Fund's strategy to
          normally invest up to 80% of its assets in securities of companies
          that have life sciences orientation, the Staff asked whether or not
          80% could be invested in derivatives, and if so, requested that the
          Registrant make that point clear to investors.

          RESPONSE: The Fund has the ability, but not the intention, to normally
          invest up to 80% of its assets in derivatives. The Fund does not
          generally invest in derivatives, although they are not precluded from
          doing so. If this changes, the Fund's Risk/Return Summary disclosure
          would be updated to include additional disclosure regarding investment
          in derivatives.

     10.  COMMENT: In regards to Janus Global Life Sciences Fund, the Staff
          asked whether the Fund has a concentration policy.

          RESPONSE: The Fund does not have a concentration policy. The Fund may
          focus its investment in "life sciences" related industry groups, but
          does not concentrate in one particular industry or industry group.

     11.  COMMENT: In each Prospectus under the section titled "Short Sales,"
          the Registrant indicates that short positions through derivative
          instruments such as options are exposed to the same risks as short
          sales. The Staff requested that the Registrant confirm that the
          derivative instruments referenced in the prospectus complies with the
          asset segregation or "cover" rules described in Investment Company Act
          Release No. 10666 (April 18, 1979).

          RESPONSE: The Registrant confirms that, to the best of its knowledge,
          the Fund has complied with asset segregation or "cover" rules with
          regards to its derivative instruments.

     12.  COMMENT: The Staff asked for clarification regarding the management of
          Janus Global Research Fund and whether disclosure as it relates to
          Item 5 of Form N-1A is appropriate.

          RESPONSE: Director of Research, James Goff oversees the team of equity
          research analysts that select investments for consideration by Mr.
          Goff and the Fund. Mr. Goff is responsible for the



          day-to-day operations of the Fund. The Registrant believes that the
          disclosure in the Management section of the Fund's Prospectus is
          consistent with Item 5 of Form N-1A.

     13.  COMMENT: With regards to the Janus Smart Portfolios, the Staff
          requested that each Fund indicate in its respective Summary Section of
          the Prospectus that it operates as a "fund of funds."

          RESPONSE: The Registrant acknowledges the comment and has updated the
          disclosure as appropriate.

     14.  COMMENT: With regards to the Janus High Yield Fund, the Staff asked
          for clarification regarding the reference to "other high yielding
          securities" in the Fund's Principal Investment Strategies section of
          the Prospectus.

          RESPONSE: The Registrant responds by noting that the Fund has included
          the phrase "other high-yielding securities" to include the variety of
          instruments that may have high yield exposure such as derivative
          contracts, which may not be rated by a National Recognized Statistical
          Rating Organization.

     15.  COMMENT: With respect to Janus Short-Term Bond Fund, the Staff asked
          how the policy of investing in intermediate-term fixed-income
          securities is consistent with the Fund's name.

          RESPONSE: The adopting release for Rule 35d-1 (the Fund Names Rule)
          notes that the Division of Investment Management has required funds
          with "short-term" in their names to maintain a dollar-weighted average
          maturity of no more than three years. Although this Fund may invest to
          some extent in intermediate-term fixed income securities, consistent
          with the Division's policy, the Fund's policy disclosed in the
          Prospectus is to maintain an average-weighted effective maturity of
          three years or less under normal circumstances.

SAI Comments

     16.  COMMENT: In the section titled "Investment Policies and Restrictions
          Applicable to All Funds," with respect to Janus Global Life Sciences
          Fund, the policies state that Janus Global Life Sciences Fund "may
          invest 25% or more of its total assets, in aggregate, in the following
          industry groups: health care, pharmaceuticals, agriculture,
          cosmetics/personal care, and biotechnology." The Staff indicated that
          the word "may" ought to be replaced with "will."

          RESPONSE: The Registrant acknowledges the comment and has updated the
          disclosure to include the phrase "will normally." The Fund does not
          have a 1940 Act concentration policy but has a fundamental policy that
          it "will normally" invest in the industry groups referenced above.

     17.  COMMENT: With respect to the "Investment Company Securities" section
          of the SAI, the Staff asked if the Registrant's reference to "other
          index-based investments" could include hedge funds.

          RESPONSE: The Registrant does not currently contemplate investing in
          hedge funds.



     18.  COMMENT: With respect to the "Net Asset Value Determination" section
          of the SAI, the Staff requested that the Registrant explain how far
          back in time it would go when reprocessing shareholder transactions in
          situations where an error has occurred in a Fund's NAV calculation.

          RESPONSE: The Fund will reprocess shareholder transactions only if
          they meet a certain threshold. If the error is greater than 1/2 of 1%
          of the Fund's net asset value per share, transactions will be
          reprocessed for any shareholder account with respect to which the
          total impact of the error was $10.00 or more. Qualifying transactions
          will be reprocessed back to the date of the error. Multiple-day errors
          are viewed as one error (not multiple errors).

     19.  COMMENT: The Staff requested that the Registrant provide a Tandy
          representation in a response letter to be filed as correspondence
          separate from the filing.

          RESPONSE: The Registrant provides its response below.

The Registrant acknowledges responsibility for the adequacy and accuracy of the
disclosure in the filings. In addition, the Registrant acknowledges that Staff
comments, or changes to disclosure in response to Staff comments in the filings
reviewed by the Staff, do not foreclose the Commission from taking any action
with respect to the filing.

If you have any concerns regarding the above responses, please call me at (303)
336-4562. Thank you for your assistance in this matter.

Regards,


/s/ Rodney DeWalt

Rodney DeWalt
Legal Counsel

cc: Stephanie Grauerholz-Lofton, Esq.
    Robin Nesbitt, Esq.
    Donna Brungardt