EXHIBIT 10

                                 FIRST AMENDMENT
                      TO MASTER LETTER OF CREDIT AGREEMENT

     This First Amendment to Master Letter of Credit Agreement (this
"Amendment") is dated as of April 29, 2005 by and between USG CORPORATION, a
Delaware corporation ("Applicant"), and LASALLE BANK NATIONAL ASSOCIATION
("Bank").

                                   WITNESSETH:

     WHEREAS, Applicant and Bank are parties to that certain Master Letter of
Credit Agreement, dated as of June 11, 2003 (as it has been and may further be
amended, restated, modified or supplemented and in effect from time to time, the
"Agreement");

     WHEREAS, Applicant is a debtor and debtor-in-possession in Chapter 11 case
(case no. 01-2094) in the United States Bankruptcy Court (the "Court") for the
District of Delaware;

     WHEREAS, Applicant has requested that Bank amend the Agreement in certain
respects, as more fully set forth herein, and Bank is agreeable to such request
subject to the terms and conditions set forth herein;

     NOW, THEREFORE, the parties hereto hereby agree as follows:

     1. DEFINITIONS. Capitalized terms used in this Amendment and not otherwise
defined herein are used with the meanings given such terms in the Agreement.

     2. AMENDMENTS. The Agreement is hereby amended as follows:

          (a) By amending and restating Section R-1 as follows:

                    "R-1 Letter of Credit Commitment.

                    (a) Prior to April 30, 2008 and provided that no Event of
               Default then exists, Bank will issue Letters of Credit with an
               aggregate stated amount not in excess of $175,000,000.00 at any
               one time (the "Letter of Credit Commitment") in each case
               containing such terms and conditions as are reasonably
               satisfactory to Bank, provided, however, no Letter of Credit
               shall have an expiry date later than the earlier to occur of (a)
               one year after the date of issuance thereof, and (b) April 30,
               2009."

                    (b) At Applicant's option, the Letter of Credit Commitment
               shall terminate on the effective date of Applicant's chapter 11
               plan of reorganization (the "Early Termination Date"). Applicant
               may exercise such termination option by issuing written notice to
               Bank of Applicant's intent to terminate the Letter of Credit
               Commitment at least three business days' before the effective
               date of such chapter 11 plan of reorganization. Notwithstanding
               anything to the contrary herein, no fees payable under Subsection
               R-2(b) hereof shall accrue after the Early Termination Date. All

               Required Collateral held by Bank for any Letter of Credit shall
               be promptly returned to Applicant promptly after Bank receives
               such outstanding Letter of Credit and a signed letter from the
               applicable beneficiary, in the form of EXHIBIT A attached hereto
               or such other evidence in form reasonably acceptable to Bank,
               which evidences such beneficiary's consent to cancel such Letter
               of Credit."

          (b) By amending and restating Subsections R-2(a) and (b) as follows:

                    "(a) LC Fee. One-half of one percent (0.5%) of the undrawn
               amount of each Letter of Credit (computed for the actual number
               of days elapsed on the basis of a year of 360 days), payable in
               arrears on the last day of each quarter and on April 30, 2009
               (for any period then ending for which such fee shall not have
               previously been paid). Notwithstanding anything to the contrary
               herein, no fees payable under this Subsection R-2(a) shall accrue
               for any Letter of Credit after the date Bank receives such Letter
               of Credit and a signed letter from the applicable beneficiary, in
               the form of EXHIBIT A attached hereto or such other evidence in
               form reasonably acceptable to Bank, which evidences such
               beneficiary's consent to cancel such Letter of Credit."

                    "(b) Non-Use Fee. One-quarter of one percent (0.25%) of the
               unused amount of the Letter of Credit Commitment, payable in
               arrears on the last day of each quarter and on April 30, 2009
               (for any period then ending for which such non-use fee shall not
               have previously been paid). For purposes of calculating usage
               under this subsection, the Letter of Credit Commitment shall be
               deemed used to the extent of the stated face amount of all
               Letters of Credit. The non-use fee shall be computed for the
               actual number of days elapsed on the basis of a year of 360
               days."

          (c) By amending and restating Subsection R-3(a) as follows:

                    "(a) The obligation of Bank to issue any Letters of Credit
               is subject to the following:

                         (i) Applicant pledging cash collateral in a trust
                    account with Bank (time deposit open account or certificate
                    of deposit) to Bank for all outstanding Letters of Credit
                    pursuant to documentation satisfactory to Bank in the amount
                    of 103% of the face amount of all outstanding Letters of
                    Credit; provided, however, for cash collateral requirements
                    in excess of $125,000,000, at Bank's sole discretion, Bank
                    will permit the pledge of Cash Equivalent Investments (in
                    lieu of cash) maintained in a trust account with Bank
                    pursuant to documentation satisfactory to Bank which, when
                    multiplied by the Bank's advance rates for collateral of
                    such type (as from time to time determined by the Bank),
                    will equal or exceed 103% of the face amount of all
                    outstanding Letters of Credit. As used herein, "Cash
                    Equivalent Investments" shall mean, at any time, (a) any
                    evidence of


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                    debt, maturing not more than one year after such time,
                    issued by the United States Government, (b) any certificate
                    of deposit, maturing not more than six months after such
                    time, that are issued or sold by LaSalle Bank or its holding
                    company or, upon Bank's sole discretion, by a commercial
                    banking institution that is a member of the Federal Reserve
                    System and has combined capital and surplus and undivided
                    profits of not less than $500,000,000 and rated at least A
                    by Standard & Poor's Ratings Group or A or A-1 by Moody's
                    Investors Service, Inc., and (c) any mutual fund that is
                    regulated by the Investment Company Act of 1940 which
                    invests solely in the investments described in clauses (a)
                    or (b) above.

                         (ii) The representations and warranties of the
                    Applicant shall be true and correct as of such requested
                    date as though made on the date thereof.

                         (iii) No Event of Default or Unmatured Event of Default
                    shall have then occurred and be continuing or will result
                    from such issuance.

                    For the elimination of any doubt, the Bank's obligation to
               issue any Letter of Credit is subject to the condition precedent
               that the Applicant deliver cash collateral to Bank in the amount
               of 103% of the face amount of the proposed Letter of Credit (the
               "Required Collateral"). Any commitment the Bank may have to issue
               a particular Letter of Credit hereunder is unconditionally
               cancelable by the Bank absent the prior delivery by the Applicant
               to the Bank of the Required Collateral.

     3. CONDITIONS TO EFFECTIVENESS. This Amendment shall become effective on
the date on which the Bank shall have receiving all of the following:

          (a) This Amendment, which has been duly executed and delivered by
     Applicant.

          (b) That certain First Amendment to Pledge Agreement dated the date
     hereof by and between Applicant and Bank, which has been duly executed and
     delivered by Applicant.

          (c) a certificate of the Secretary of Applicant stating that there has
     been no change in the Certificate of Incorporation or By-Laws of Applicant
     since such documents were last delivered to the Bank and that there has
     been no change in the officers of Applicant since the last incumbency
     certificate for Applicant was delivered to the Bank.

          (d) good standing certificates for Applicant from the State of
     Illinois and the State of Delaware.

          (e) Payment by Applicant of all fees, costs and expenses to the extent
     then due and payable.


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          (f) a copy of an order from the Court, which approves the Agreement,
     as amended by this Amendment and that certain Pledge Agreement dated as of
     June 11, 2003 by and between Applicant and Bank, as amended, and no notice
     of appeal has been filed.

     4. MISCELLANEOUS.

          (a) Applicant hereby agrees to pay all of Bank's costs and reasonable
     expenses, including, without limitation, reasonable attorneys' fees,
     related to this Amendment.

          (b) This Amendment may be executed in one or more counterparts, each
     of which shall be deemed to be an original, but all of which shall together
     constitute but one and the same document.

          (c) This Amendment shall be binding upon and inure to the benefit of
     the parties hereto and their respective successors and assigns.

          (d) Section captions and headings used in this Amendment are for
     convenience only and are not part of and shall not affect the construction
     of this Amendment.

          (e) This Amendment shall be a contract made under and governed by the
     laws of the State of Illinois, without regard to conflict of laws
     principles. Whenever possible, each provision of this Amendment shall be
     interpreted in such a manner as to be effective and valid under applicable
     law, but if any provision of this Amendment shall be prohibited by or
     invalid under such law, such provision shall be ineffective to the extent
     of such prohibition or invalidity, without invalidating the remainder of
     such provision or the remaining provisions of this Amendment.

          (f) From and after the date of execution of this Amendment, any
     reference to the Agreement contained in any notice, request, certificate or
     other instrument, document or agreement shall be deemed to include this
     Amendment unless the context shall otherwise require.

          (g) Except as expressly set forth herein, nothing in this Amendment is
     intended to or shall be deemed to have amended the Agreement, which is
     hereby reaffirmed in all respects. The Agreement, as amended hereby, and
     each of the other related agreements remain in full force and effect and
     are hereby reaffirmed in all respects.

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first set forth above.

USG CORPORATION, a Delaware             LASALLE BANK NATIONAL ASSOCIATION,
corporation                             a national banking association


By: /s/ Karen L. Leets                  By: /s/ William B. McKinley
    ---------------------------------       ------------------------------------
Its: Vice President and Treasurer           William B. McKinley
                                            First Vice President


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                                 FIRST AMENDMENT
                               TO PLEDGE AGREEMENT

     This First Amendment to Pledge Agreement (this "Amendment") is dated as of
April 29, 2005 by and between USG CORPORATION, a Delaware corporation
(the"Assignor"), and LASALLE BANK NATIONAL ASSOCIATION (the "Bank").

                                   WITNESSETH:

     WHEREAS, Assignor and the Bank are parties to that certain Pledge
Agreement, dated as of June 11, 2003 (as it has been and may further be amended,
restated, modified or supplemented and in effect from time to time, the "Pledge
Agreement");

     WHEREAS, Assignor has requested that the Bank amend the Pledge Agreement in
certain respects, as more fully set forth herein, and the Bank is agreeable to
such request subject to the terms and conditions set forth herein;

     NOW, THEREFORE, the parties hereto hereby agree as follows:

     1. DEFINITIONS. Capitalized terms used in this Amendment and not otherwise
defined herein are used with the meanings given such terms in the Pledge
Agreement.

     2. AMENDMENT. Section 3(a) of the Pledge Agreement is hereby amended and
restated as follows:

          "(a) At all times the assets of the Account shall be held in cash or
     Cash Equivalent Investments. As used herein, "Cash Equivalent Investments"
     shall mean, at any time, (i) any evidence of debt, maturing not more than
     one year after such time, issued by the United States Government, (ii) any
     certificate of deposit, maturing not more than six months after such time,
     that are issued or sold by LaSalle Bank or its holding company or, upon
     Bank's sole discretion, by a commercial banking institution that is a
     member of the Federal Reserve System and has combined capital and surplus
     and undivided profits of not less than $500,000,000 and rated at least A by
     Standard & Poor's Ratings Group or A or A-1 by Moody's Investors Service,
     Inc., and (iii) any mutual fund that is regulated by the Investment Company
     Act of 1940 which invests solely in the investments described in clauses
     (i) or (ii) above."

     3. MISCELLANEOUS.

          (a) Assignor hereby agrees to pay all of the Bank's costs and
     reasonable expenses, including, without limitation, attorneys' fees,
     related to this Amendment.

          (b) This Amendment may be executed in one or more counterparts, each
     of which shall be deemed to be an original, but all of which shall together
     constitute but one and the same document.

          (c) This Amendment shall be binding upon and inure to the benefit of
     the parties hereto and their respective successors and assigns.


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          (d) Section captions and headings used in this Amendment are for
     convenience only and are not part of and shall not affect the construction
     of this Amendment.

          (e) This Amendment shall be a contract made under and governed by the
     laws of the State of Illinois, without regard to conflict of laws
     principles. Whenever possible, each provision of this Amendment shall be
     interpreted in such a manner as to be effective and valid under applicable
     law, but if any provision of this Amendment shall be prohibited by or
     invalid under such law, such provision shall be ineffective to the extent
     of such prohibition or invalidity, without invalidating the remainder of
     such provision or the remaining provisions of this Amendment.

          (f) From and after the date of execution of this Amendment, any
     reference to the Pledge Agreement contained in any notice, request,
     certificate or other instrument, document or agreement shall be deemed to
     include this Amendment unless the context shall otherwise require.

          (g) Except as expressly set forth herein, nothing in this Amendment is
     intended to or shall be deemed to have amended the Pledge Agreement, which
     is hereby reaffirmed in all respects. The Pledge Agreement, as amended
     hereby, and each of the other related agreements remain in full force and
     effect and are hereby reaffirmed in all respects.

     IN WITNESS WHEREOF, the parties have executed this Amendment as of the date
first set forth above.

USG CORPORATION, a Delaware             LASALLE BANK NATIONAL ASSOCIATION,
corporation                             a national banking association


By: /s/ Karen L. Leets                  By: /s/ William B. McKinley
    ---------------------------------       ------------------------------------
Its: Vice President and Treasurer           William B. McKinley
                                            First Vice President


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