<PAGE>


                                                                       EXHIBIT 4

                                 FIRST AMENDMENT

                  FIRST AMENDMENT, dated as of May 3, 2000 (this "Amendment"),
to the 364-Day Credit Agreement, dated as of May 5, 1999 (as amended,
supplemented or otherwise modified from time to time, the "Agreement"), among W.
R. Grace & Co.-Conn., a Connecticut corporation (the "Company"), W. R. Grace &
Co., a Delaware corporation (the "Parent"), the several banks from time to time
parties thereto (the "Banks"), Bank of America, N.A. (formerly known as Bank of
America National Trust and Savings Association), a national bank, as syndication
agent (in such capacity, the "Syndication Agent"), The Chase Manhattan Bank, a
New York banking corporation, as administrative agent for the Banks thereunder
(in such capacity, the "Administrative Agent"), Chase Securities Inc., as book
manager (in such capacity, the "Book Manager") and First Union National Bank, as
documentation agent (in such capacity, the "Documentation Agent").

                              W I T N E S S E T H:

                  WHEREAS, pursuant to the Agreement, the Banks have agreed to
make, and have made, certain loans and other extensions of credit to the
Borrowers; and

                  WHEREAS, the Borrowers have requested, and, upon this
Amendment becoming effective, the Banks have agreed, that certain provisions of
the Agreement be amended in the manner provided for in this Amendment.

                  NOW, THEREFORE, for valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, and in consideration of the
premises and mutual agreements contained herein, the parties hereto hereby agree
as follows:

                              SECTION I. AMENDMENTS

                  1.1 Defined Terms. Unless otherwise defined herein,
capitalized terms which are defined in the Agreement are used herein as defined
therein.

                  1.2  Amendment to subsection 1.1.  Subsection 1.1 of the
Agreement is hereby amended:

                  (a) by deleting therefrom the existing definition of
"Applicable Margin" and by substituting therefor the following:

                  "Applicable Margin": for any day on which the long term senior
         unenhanced, unsecured debt of the Company is rated by both S&P and
         Moody's, the rate per annum under the caption "Margin" (a "Margin
         Rate") set forth below opposite the S&P and Moody's ratings applicable
         to such debt on such day (or, if such ratings are set opposite two
         different Margin Rates, then the Applicable Margin shall be the lower
         of said two Margin Rates):


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                  Margin           S&P                        Moody's
                  ------           ---                        -------

                  1.00%            BB or lower                Ba2 or lower

                  .800%            BB+                        Ba1

                  .575%            BBB-                       Baa3

                  .475%            BBB or higher              Baa2 or higher

         provided that if on any day (i) the long term senior unenhanced,
         unsecured debt of the Company is rated by only one of either S&P or
         Moody's, the Applicable Margin will be determined based on the rating
         by such rating agency, (ii) the long term senior unenhanced, unsecured
         debt of the Company is rated by neither S&P nor Moody's, the Applicable
         Margin will be determined based on the rating of such debt by Duff &
         Phelps, Fitch or another nationally recognized statistical rating
         organization agreed to by and among the Company, the Administrative
         Agent and the Majority Banks (each, a "Substitute Rating Agency") and
         will be the Margin Rate set forth above opposite the S&P and Moody's
         ratings comparable to such Substitute Rating Agency's rating of such
         debt on such date and (iii) the long term senior unenhanced, unsecured
         debt of the Company is rated by none of S&P, Moody's or any Substitute
         Rating Agency, the Company, the Administrative Agent and the Banks will
         negotiate in good faith to determine an alternative basis for
         calculating the Applicable Margin consistent with the table set forth
         above and, if agreement on such alternative basis is not reached within
         30 days, the Applicable Margin will be calculated on an alternative
         basis determined by the Administrative Agent and the Banks in their
         reasonable discretion consistent with the table above, and until such
         alternative basis is determined the Applicable Margin will be the
         Applicable Margin last determined as provided in the table above; and
         provided, further, that (a) if on any day the aggregate Loan
         Outstandings of all of the Banks plus the Aggregate Outstanding
         Bilateral Option Loans is greater than 25% of the Commitments but less
         than or equal to 50% of the Commitments, the Applicable Margin in
         effect on each such day shall be increased by .125% or (b) if on any
         day the aggregate Loan Outstandings of all of the Banks plus the
         Aggregate Outstanding Bilateral Option Loans is greater than 50% of all
         of the Commitments, the Applicable Margin in effect on each such day
         shall be increased by .25%.

                  (b) by deleting therefrom the existing definition of
"Termination Date" and by substituting therefor the following

                  "Termination Date": May 2, 2001 or such later date to which
the Termination Date may be extended pursuant to subsection 2.4.

                  1.3 Amendment to subsection 6.6. Subsection 6.6 of the
Agreement is hereby amended:

                  (a) by deleting therefrom the following: "December 31, 1998"
where it appears therein and

                  (b) by inserting in lieu thereof "December 31, 1999".

                  1.4 Amendment to subsection 6.16. Subsection 6.16 of the
Agreement and any reference to such subsection contained in the Agreement
(including, without limitation, in Exhibit I to the Agreement) are hereby
deleted in their entireties.

                  1.5 Amendment to subsection 8.2. Subsection 8.2(b) of the
Agreement is hereby amended:

                  (a) by deleting therefrom the following: ", (ii) to the best
of such Officer's knowledge, the representation and warranty contained in
subsection 6.16 is true and correct as of the date of delivery of such financial
statements and certificate and (iii)" and

                  (b) by inserting in lieu thereof "and (ii)".

                  1.6 Amendment to subsection 8.9. Subsection 8.9 of the
Agreement is hereby deleted in its entirety.



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                  1.7 Amendment to Schedule 1. Schedule 1 to the Agreement is
hereby deleted in its entirety and replaced with the new Schedule 1 attached to
this Amendment.

                            SECTION II. MISCELLANEOUS

                  2.1 Conditions to Effectiveness of Amendment. This Amendment
shall become effective as of the date first set forth above upon:

                  (a) the Administrative Agent having received counterparts of
this Amendment duly executed and delivered by the Company, the Parent, the
Administrative Agent and the each of the Banks; and

                  (b) the Administrative Agent having received, on behalf of
itself, the Banks and the Book Manager, the fees specified in Section 2.2 of
this Amendment.

                  2.2 Fees. The Company shall pay to the Administrative Agent,
for the account of the Administrative Agent, the Banks and the Book Manager, the
fees in the amounts and on the terms previously agreed to in writing by the
Parent, the Administrative Agent and the Book Manager.

                  2.3 Representations and Warranties. Each of the Loan Parties,
as of the date hereof and after giving effect to the amendments contained
herein, hereby confirms, reaffirms and restates the representations and
warranties made by it in Section 6 of the Agreement and in any other Loan
Document to which it is a party; provided that each reference to the Agreement
therein shall be deemed to be a reference to the Agreement after giving effect
to this Amendment.

                  2.4 Limited Effect. The execution, delivery and effectiveness
of this Amendment shall not, except as expressly provided herein, operate as a
waiver of any right, power or remedy of any Bank or the Administrative Agent
under the Agreement, nor constitute a waiver or amendment of any provisions of
the Agreement. Except as expressly modified herein, all of the provisions and
covenants of the Agreement are and shall continue to remain in full force and
effect in accordance with the terms thereof and are hereby in all respects
ratified and confirmed.

                  2.5 Counterparts. This Amendment may be executed by one or
more of the parties hereto in any number of separate counterparts (which may
include counterparts delivered by facsimile transmission) and all of said
counterparts taken together shall be deemed to constitute one and the same
instrument. Any executed counterpart delivered by facsimile transmission shall
be effective as for all purposes hereof.

                  2.6 GOVERNING LAW. THIS AMENDMENT AND THE RIGHTS AND
OBLIGATIONS OF THE PARTIES HEREUNDER SHALL BE GOVERNED BY, AND CONSTRUED AND
INTERPRETED IN ACCORDANCE WITH, THE LAW OF THE STATE OF NEW YORK.

                                  (End of Page)


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                  IN WITNESS WHEREOF, the parties hereto have caused this
Amendment to be duly executed and delivered by their respective proper and duly
authorized officers as of the day and year first above written.

                                   W. R. GRACE & CO.-CONN.

                                   By:
                                      -----------------------------------
                                      Title:

                                   W. R. GRACE & CO.

                                   By:
                                      -----------------------------------
                                      Title:

                                   THE CHASE MANHATTAN BANK,
                                   as Administrative Agent and as a Bank

                                   By:
                                      -----------------------------------
                                      Title:

                                   BANK OF AMERICA, N.A.,
                                   as Syndication Agent and as a Bank

                                   By:
                                      -----------------------------------
                                      Title:

                                   FIRST UNION NATIONAL BANK,
                                   as Documentation Agent and as a Bank

                                   By:
                                      -----------------------------------
                                      Title:


                                   ABN AMRO BANK N.V.

                                   By:
                                      -----------------------------------
                                      Title:

                                   By:
                                      -----------------------------------
                                      Title:



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                                   BANK HAPOALIM B.M.

                                   By:
                                      -----------------------------------
                                      Title:

                                   CREDIT SUISSE FIRST BOSTON

                                   By:
                                      -----------------------------------
                                      Title:

                                   By:
                                      -----------------------------------
                                      Title:

                                   DRESDNER BANK AG, NEW YORK AND GRAND
                                   CAYMAN BRANCHES

                                   By:
                                      -----------------------------------
                                      Title:

                                   By:
                                      -----------------------------------
                                      Title:


                                   THE BANK OF NEW YORK

                                   By:
                                      -----------------------------------
                                      Title:

                                   THE BANK OF NOVA SCOTIA

                                   By:
                                      -----------------------------------
                                      Title:

                                   THE NORTHERN TRUST COMPANY

                                   By:
                                      -----------------------------------
                                      Title:


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                                   WACHOVIA BANK, N.A.

                                   By:
                                      -----------------------------------
                                      Title:


                                                                      SCHEDULE I
                                                                      ----------
                                   Commitments
                                   -----------

BANK                                                                 COMMITMENT
----                                                                 ----------

The Chase Manhattan Bank                                             $28,000,000

Bank of America, N.A.                                                $28,000,000

First Union National Bank                                            $28,000,000

Credit Suisse First Boston                                           $25,000,000

Dresdner Bank AG, New York and Grand Cayman Branches                 $24,000,000

The Bank of Nova Scotia                                              $24,000,000

ABN AMRO Bank N.V.                                                   $19,500,000

The Bank of New York                                                 $19,500,000

The Northern Trust Company                                           $19,500,000

Wachovia Bank, N.A.                                                  $19,500,000

Bank Hapoalim                                                        $15,000,000

TOTAL:                                                              $250,000,000
                                                                    ============