Exhibit 10.1

                                                                        ANNEX I

            AMENDMENT NO. 4 TO AMENDED AND RESTATED CREDIT AGREEMENT

         THIS AMENDMENT NO. 4 TO AMENDED AND RESTATED CREDIT AGREEMENT (this
"AMENDMENT"), dated as of June 5, 2002, among Charles River Laboratories, Inc.,
a Delaware corporation (the "BORROWER"), Charles River Laboratories
International, Inc. (f/k/a Charles River Laboratories Holdings, Inc.), a
Delaware corporation ("HOLDCO"), Credit Suisse First Boston, as lead arranger,
as sole book runner and as syndication agent (in such capacity, the "SYNDICATION
AGENT") for the Lenders (as defined below), and Fleet National Bank, as
administrative agent (the "ADMINISTRATIVE AGENT") for the Lenders.

                              W I T N E S S E T H:

         WHEREAS, the Borrower, certain financial institutions (together with
their respective successors and assigns, the "LENDERS"), the Syndication Agent
and the Administrative Agent are parties to the Amended and Restated Credit
Agreement, dated as of February 2, 2001 (as heretofore modified and supplemented
and in effect from time to time, the "EXISTING CREDIT AGREEMENT" and as further
amended hereby, the "CREDIT AGREEMENT");

         WHEREAS, the Borrower desires to acquire (the "BIOLABS ACQUISITION")
all of the issued and outstanding Capital Stock of Biological Laboratories
Europe Ltd., a company organized under the laws of the Republic of Ireland
("BIOLABS") pursuant to a stock purchase agreement (the "BIOLABS PURCHASE
AGREEMENT"), to be entered into by BioLabs and the Borrower for a gross
transaction value not to exceed euro 25,000,000 (exclusive of additional share
consideration contingently payable to certain stockholders of BioLabs as
provided for in the BioLabs Purchase Agreement but in any event not to exceed
euro 2,000,000);

         WHEREAS, the Borrower desires to enter into a joint venture arrangement
(the "PROTEOMICS JOINT VENTURE") with Proteome Systems Ltd., a company organized
under the laws of Australia ("PROTEOME"), for the purpose of providing
proteomics testing services on a contract basis to the global pharmaceutical
industry;

         WHEREAS, the Proteomics Joint Venture will be operated through a
to-be-formed Delaware corporation to be known as Charles River Proteomics, Inc.
("CHARLES RIVER PROTEOMICS") of which the Borrower will own 60% of the Capital
Stock and Proteome (or one of its affiliates) will own the remaining Capital
Stock; and

         WHEREAS, the Borrower and Holdco desire, and the Lenders are willing,
on the terms and subject to the conditions hereinafter set forth, to amend the
Existing Credit Agreement as set forth herein to permit them to do so;



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

                                     PART I
                                   DEFINITIONS

         SUBPART 1.1 CERTAIN DEFINITIONS. Unless otherwise defined herein or the
context otherwise requires, terms used in this Amendment, including its preamble
and recitals, have the following meanings (such meanings to be equally
applicable to the singular and plural forms thereof):

         "ADMINISTRATIVE AGENT" is defined in the PREAMBLE.

         "AMENDMENT" is defined in the PREAMBLE.

         "AMENDMENT EFFECTIVE DATE" is defined in SUBPART 3.1.

         "BIOLABS" is defined in the SECOND RECITAL.

         "BIOLABS ACQUISITION" is defined in the SECOND RECITAL.

         "BIOLABS PURCHASE AGREEMENT" is defined in the SECOND RECITAL.

         "BORROWER" is defined in the PREAMBLE.

         "CHARLES RIVER PROTEOMICS" is defined in the FOURTH RECITAL.

         "CREDIT AGREEMENT" is defined in the FIRST RECITAL.

         "EXISTING CREDIT AGREEMENT" is defined in the FIRST RECITAL.

         "HOLDCO" is defined in the PREAMBLE.

         "LENDERS" is defined in the FIRST RECITAL.

         "PROTEOMICS JOINT VENTURE" is defined in the FOURTH RECITAL.

         "PROTEOME" is defined in the third recital.

         "SYNDICATION AGENT" is defined in the PREAMBLE.

         SUBPART 1.2 OTHER DEFINITIONS. Unless otherwise defined herein or the
context otherwise requires, terms used in this Amendment, including its preamble
and recitals, have the meanings set forth in the Existing Credit Agreement. Each
reference to "hereof", "hereunder", "herein" and "hereby" and each other similar
reference and each reference to "this Agreement" and each other similar
reference contained in the Existing Credit Agreement shall from and after the
Amendment Effective Date refer to the Credit Agreement.

                                      -2-


                                    PART II
                     AMENDMENTS TO existing CREDIT AGREEMENT

         Effective on (and subject to the occurrence of) the Amendment No. 4
Effective Date, the Existing Credit Agreement is hereby amended in accordance
with this Part II. Except to the extent amended by this Amendment, the Existing
Credit Agreement is and shall continue to be in full force and effect and is
hereby ratified and confirmed in all respects.

         SUBPART 2.1 AMENDMENTS TO ARTICLE I. Article I of the Existing Credit
Agreement is amended as set forth in this Subpart 2.1:

         (a)      Section 1.1 is hereby amended by inserting the following
definitions in such Section in the appropriate alphabetical order:

         "AMENDMENT NO. 4" means Amendment No. 4 to Amended and Restated Credit
Agreement, dated as of June 5, 2002, among the Borrower, Holdco and the Agents,
which amendment was consented to by the Lenders constituting the Required
Lenders.

         "AMENDMENT NO. 4 EFFECTIVE DATE" is defined in Part III of Amendment
No. 4.

         "BIOLABS" is defined in Amendment No. 4.

         "BIOLABS ACQUISITION" is defined in Amendment No. 4.

         "BIOLABS PURCHASE AGREEMENT" is defined in Amendment No. 4.

         "CHARLES RIVER PROTEOMICS" is defined in Amendment No. 4.

         "JV LOAN INVESTMENTS" is defined in Section 7.2.5(r).

         "PROTEOME" is defined in Amendment No. 4.

         "PROTEOMICS JOINT VENTURE" is defined in Amendment No. 4.

         (b) The definition of "Unrestricted Subsidiary" is hereby amended by
inserting the words "the Proteomics Joint Venture and" immediately following the
word "means" in the first sentence thereof.

         SUBPART 2.2 AMENDMENTS TO ARTICLE VII. Article VII of the Existing
Credit Agreement is hereby amended as set forth in this Subpart 2.2.

         (a) Section 7.1.7 of the Existing Credit Agreement is hereby amended by
inserting the following sentence at the end thereof:

         "Notwithstanding the foregoing, the Borrower shall promptly deliver, to
the Administrative Agent, under a Pledge Agreement, certificates representing
all of the issued and outstanding shares of Capital Stock of Charles River
Proteomics owned by the Borrower, which shall constitute not less than 60% of
all issued and outstanding shares of Capital Stock of Charles River Charles
River Proteomics."

                                      -3-


         (b) Section 7.2.2 of the Existing Credit Agreement is hereby amended
by:

                  (i) deleting the word "and" following the semicolon at the end
         of clause (k) thereto,

                  (ii) deleting the period at the end of clause (l) thereto and
         adding a semicolon and the word "and" in lieu thereof, and

                  (iii) inserting new clause (m) to read in its entirety:

         "(m) Contingent Liabilities of the Borrower arising as a result of the
Borrower's guaranty of Indebtedness of the type described in clause (a) of the
definition of Indebtedness incurred by the Proteomics Joint Venture in an
aggregate principal amount not to exceed at any time outstanding $3,000,000
MINUS the aggregate principal or face amount of JV Loan Investments outstanding
at such time."

         (c) Section 7.2.5 of the Existing Credit Agreement is hereby amended
by:

                  (i) deleting the word "and" at the end of clause (q) thereto;

                  (ii) reordering clauses (r), (s) and (t) thereto to be new
         clauses (t), (u) and (v), respectively; and

                  (iii) inserting the following new clauses (r) and (s) to read
         in their entirety:

                  "(r) (x) Investments (in cash or in kind) in the Proteomics
         Joint Venture (other than Investments described in CLAUSE (y) of this
         CLAUSE (r)) in an aggregate amount not to exceed $6,000,000 and (y)
         Investments by the Borrower in the Proteomics Joint Venture ("JV LOAN
         INVESTMENTS") consisting of loans or advances in an aggregate principal
         or face amount at any time outstanding not to exceed $3,000,000 MINUS
         the outstanding aggregate principal amount of Indebtedness guaranteed
         by the Borrower pursuant to CLAUSE (m) of SECTION 7.2.2, in each case
         over the term of this Agreement; PROVIDED, that on or prior to the
         making of such Investment, the Borrower pledges the Capital Stock of
         Charles River Proteomics to the Administrative Agent for the benefit of
         the Secured Parties;

                  (s) Investments in BioLabs by the Borrower in connection with
         the BioLabs Acquisition in accordance with BioLabs Purchase Agreement,
         which agreement (i) shall, on the Amendment No. 4 Effective Date, be in
         form and substance reasonably satisfactory to the Agents and (ii) shall
         not have been modified or waived in any material respect, nor shall
         there have been any forbearance to exercise any material rights with
         respect to any of the terms or provisions relating to the conditions to
         the consummation of such acquisition as set forth therein unless
         otherwise agreed to by the Agents); PROVIDED, that (A) BioLabs becomes
         a wholly-owned Restricted Subsidiary of the Borrower, (B) the
         requirements of Sections 7.1.7(b) and 7.1.8(c) (as such Sections relate
         to the pledge by the Borrower to the Administrative Agent of 65% of the
         issued and outstanding Capital Stock of BioLabs) shall have been
         satisfied in accordance with the terms thereof within 30 days of the
         consummation of the BioLabs Acquisition, (C) such

                                      -4-


         acquisition shall be consummated for gross consideration not exceeding
         euro 25,000,000 (exclusive of additional share consideration
         contingently payable to certain stockholders of BioLabs as provided for
         in the BioLabs Purchase Agreement but in any event not to exceed euro
         2,000,000) and (D) within 30 days of the consummation of the BioLabs
         Acquisition, the Borrower will deliver a Foreign Pledge Agreement with
         respect to the 65% of the issued and outstanding Capital Stock of
         BioLabs;".

         (d) Clause (b) of Section 7.2.8 is hereby amended by deleting the word
"or" following the reference to clause "(q)" and replacing it with a comma and
inserting the following after the reference to clause (r) therein: ", (s) or
(t)".

                                    PART III
                           CONDITIONS TO EFFECTIVENESS

         SUBPART 3.1 AMENDMENT NO. 4 EFFECTIVE DATE. This Amendment shall become
effective as of the date (the "AMENDMENT NO.4 EFFECTIVE DATE") when each of the
conditions set forth in this Part have been satisfied

         SUBPART 3.2 EXECUTION OF COUNTERPARTS, ETC. The Agents shall have
received counterparts of this Amendment, duly executed by the Borrower, Holdco,
the Syndication Agent and the Administrative Agent on behalf of the Required
Lenders who shall have delivered to the Administrative Agent their written
consent to the amendments, as explicitly set forth herein and subject to the
terms hereof.

         SUBPART 3.3 FEES, EXPENSES, ETC. The Agents shall have received all
fees, costs and expenses due and payable pursuant to Section 10.3 of the
Existing Credit Agreement to the extent then invoiced.

         SUBPART 3.4 LEGAL DETAILS, ETC. All documents executed or submitted
pursuant hereto shall be reasonably satisfactory in form and substance to the
Agents. The Agents shall have received all information, and such counterpart
originals or such certified or other copies of such materials, as the Agents or
its counsel may reasonably request. All legal matters incident to the
transactions contemplated by this Amendment shall be reasonably satisfactory to
the Agents.

                                    PART IV
                         REPRESENTATIONS AND WARRANTIES

         SUBPART 4.1 BORROWER AND HOLDCO REPRESENTATIONS AND WARRANTIES. The
delivery of an executed counterpart hereof by each of the Borrower and Holdco
shall constitute a representation and warranty by each such Obligor that:

         (a) on the Amendment No. 4 Effective Date, after giving effect to this
Amendment, (i) all representations, warranties and other statements set forth in
Article VI of the Existing Credit Agreement, as then amended by this Amendment,
are true and correct in all material respects as of such date, except to the
extent that such representation, warranty or statement expressly relates to an
earlier date (in which case such representation, warranty or statement shall
have been true and correct in all material respects on and as of such earlier
date) and (ii) no Default has occurred and is then continuing; and

                                      -5-


         (b) this Amendment constitutes the legal, valid and binding obligation
of each of the Borrower and Holdco enforceable in accordance with its terms
subject to the effects of bankruptcy, insolvency, fraudulent conveyance,
reorganization, moratorium and other similar laws relating to or affecting
creditors' rights generally, general equitable principles (whether considered in
a proceeding in equity or at law) and an implied covenant of good faith and fair
dealing.

         SUBPART 4.2 LOAN DOCUMENT PURSUANT TO CREDIT AGREEMENT. This Amendment
is a Loan Document executed pursuant to the Credit Agreement and shall (unless
otherwise expressly indicated therein) be construed, administered and applied in
accordance with all of the terms and provisions of the Credit Agreement, as
amended hereby.

                                     PART V
                                  MISCELLANEOUS

         SUBPART 5.1 SUCCESSORS AND ASSIGNS. This Amendment shall be binding
upon and inure to the benefit of the parties hereto and their respective
successors and assigns.

         SUBPART 5.2 COUNTERPARTS. This Amendment may be executed by the parties
hereto in several counterparts, each of which when executed and delivered shall
be an original and all of which shall constitute together but one and the same
agreement.

         SUBPART 5.3 GOVERNING LAW. THIS AMENDMENT SHALL BE GOVERNED BY, AND
CONSTRUED IN ACCORDANCE WITH, THE INTERNAL LAWS OF THE STATE OF NEW YORK.






                                      -6-


         IN WITNESS WHEREOF, the parties hereto have executed and delivered this
Amendment as of the date first above written.

BORROWER:                           CHARLES RIVER LABORATORIES, INC.

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

HOLDCO:                             CHARLES RIVER LABORATORIES
                                       INTERNATIONAL, INC. (f/k/a Charles
                                       River Laboratories Holdings, Inc.)

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

AGENTS:                             CREDIT SUISSE FIRST BOSTON, as
                                       Syndication Agent

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

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

                                    FLEET NATIONAL BANK, as Administrative Agent

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

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