Exhibit 10.1



                       FIRST AMENDMENT TO CREDIT AGREEMENT

     This FIRST AMENDMENT TO CREDIT AGREEMENT (this "Amendment") is entered into
as of September 20, 2002 among QUEST DIAGNOSTICS INCORPORATED, a Delaware
corporation (the "Borrower"), certain Subsidiaries of the Borrower as
Guarantors, the Lenders party hereto and BANK OF AMERICA, N.A., as
Administrative Agent for the Lenders (the "Administrative Agent"). Capitalized
terms used herein and not otherwise defined shall have the meanings set forth in
the Credit Agreement (as defined below).

                                    RECITALS

     WHEREAS, the Borrower, the Guarantors, the Lenders and the Administrative
Agent entered into that certain Credit Agreement dated as of June 21, 2002 (as
amended hereby and as the same may hereafter be further amended, modified or
supplemented, the "Credit Agreement");

     WHEREAS, the Credit Parties are requesting that the Lenders amend certain
terms of the Credit Agreement in order to extend the Maturity Date; and

     WHEREAS, the Lenders have agreed to amend certain terms of the Credit
Agreement in order to extend the Maturity Date, subject to the conditions set
forth below.

     NOW THEREFORE, for good and valuable consideration, the receipt and
sufficiency of which are hereby acknowledged, the parties hereto agree as
follows:

                                    AGREEMENT

     1. Amendment to Credit Agreement.

     (a) Section 1.1. The definition of "Maturity Date" set forth in Section 1.1
of the Credit Agreement is hereby amended and restated in its entirety to read
as follows:

          "Maturity Date" means (i) December 31, 2002 if the Unilab Acquisition
     is not consummated on or prior to such date or (ii) June 21, 2007 if the
     Unilab Acquisition is consummated on or prior to December 31, 2002.

     (b) Section 3.4. Section 3.4 of the Credit Agreement is hereby amended by
adding the following two sentences at the end of such Section to read as
follows:

          The Borrower agrees to pay to the Administrative Agent, for the
     account of the Lenders on a pro rata basis based on their Term Loan
     Commitment Percentage, a ticking fee equal to 0.25% per annum (the "Ticking
     Fee") calculated on the then applicable Term Loan Committed Amount (giving
     effect to any reduction thereof pursuant to Section 2.1(d)). The Ticking
     Fee shall accrue daily from October 1, 2002 to the earlier of the Funding
     Date





     or the Maturity Date and shall be payable monthly in arrears on the last
     Business Day of each month and on the Funding Date or the Maturity Date, as
     applicable.

     2. Effectiveness; Conditions Precedent. This Amendment shall be deemed to
have become effective as of the date above written upon receipt by the
Administrative Agent of copies of this Amendment duly executed by the Credit
Parties and the Lenders.

     3. Ratification of Credit Agreement. The term "Credit Agreement" as used in
each of the Credit Documents shall hereafter mean the Credit Agreement as
amended and modified by this Amendment. Except as herein specifically agreed,
the Credit Agreement, as amended by this Amendment, is hereby ratified and
confirmed and shall remain in full force and effect according to its terms. The
Credit Parties acknowledge and consent to the modifications set forth herein and
agree that this Amendment does not impair, reduce or limit any of their
obligations under the Credit Documents (including, without limitation, the
indemnity obligations set forth therein) and that this Amendment shall
constitute a Credit Document. Notwithstanding anything herein to the contrary
and without limiting the foregoing, each of the Guarantors reaffirms its
guaranty obligations set forth in the Credit Agreement.

     4. Authority/Enforceability. Each of the Credit Parties represents and
warrants as follows:

          (a) It has taken all necessary action to authorize the execution,
     delivery and performance of this Amendment.

          (b) This Amendment has been duly executed and delivered by such Person
     and constitutes such Person's legal, valid and binding obligations,
     enforceable in accordance with its terms, except as such enforceability may
     be subject to (i) bankruptcy, insolvency, reorganization, fraudulent
     conveyance or transfer, moratorium or similar laws affecting creditors'
     rights generally and (ii) general principles of equity (regardless of
     whether such enforceability is considered in a proceeding at law or in
     equity).

          (c) No consent, approval, authorization or order of, or filing,
     registration or qualification with, any court or governmental authority or
     third party is required in connection with the execution, delivery or
     performance by such Person of this Amendment.

          (d) The execution and delivery of this Amendment does not violate,
     contravene or conflict with any Requirement of Law applicable to it or any
     of its Subsidiaries.

     5. No Default. The Credit Parties represent and warrant to the Lenders that
after giving effect to this Amendment (a) the representations and warranties of
the Credit Parties set forth in Section 6 of the Credit Agreement are true and
correct as of the date hereof and (b) no event has occurred and is continuing
which constitutes a Default or an Event of Default.


                                       2





     6. Release. In consideration of entering into this Amendment, each of the
Credit Parties releases the Agents, the Lenders, and each Agent's and each
Lender's respective Affiliates, Subsidiaries, officers, employees,
representatives, agents, counsel and directors from any and all actions, causes
of action, claims, demands, damages and liabilities of whatever kind or nature,
in law or in equity, now known or unknown, suspected or unsuspected to the
extent that any of the foregoing arises from any action or failure to act with
respect to the Credit Agreement or the other Credit Documents on or prior to the
date hereof.

     7. Counterparts/Telecopy. This Amendment may be executed in any number of
counterparts, each of which when so executed and delivered shall be an original,
but all of which shall constitute one and the same instrument. Delivery of
executed counterparts of this Amendment by telecopy shall be effective as an
original and shall constitute a representation that an original shall be
delivered promptly upon request.

     8. Entirety. This Amendment and the other Credit Documents embody the
entire agreement between the parties hereto and supersede all prior agreements
and understandings, oral or written, if any, relating to the subject matter
hereof.

     9. 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 LAWS OF THE STATE OF NEW YORK.

     10. Venue; Jurisdiction; Waivers. The venue, jurisdiction, waiver of jury
trial and waiver of consequential damages provisions set forth in Sections 11.11
and 11.12 of the Credit Agreement are hereby incorporated by reference, mutatis
mutandis.

                  [remainder of page intentionally left blank]


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                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

     IN WITNESS WHEREOF, each of the parties hereto has caused a counterpart of
this Amendment to be duly executed and delivered and this Amendment shall be
effective as of the date first above written.

BORROWER:

                                        QUEST DIAGNOSTICS INCORPORATED,
                                        A Delaware corporation


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


GUARANTORS:

                                        QUEST DIAGNOSTICS HOLDINGS
                                        INCORPORATED,
                                        a Delaware corporation


                                        QUEST DIAGNOSTICS CLINICAL
                                        LABORATORIES, INC.,
                                        a Delaware corporation


                                        QUEST DIAGNOSTICS INCORPORATED,
                                        a California corporation


                                        QUEST DIAGNOSTICS INCORPORATED,
                                        a Maryland corporation


                                        QUEST DIAGNOSTICS INCORPORATED,
                                        a Michigan corporation


                                        QUEST DIAGNOSTICS OF PENNSYLVANIA, INC.,
                                        a Delaware corporation


                                        METWEST, INC.,
                                        a Delaware corporation


                                        NICHOLS INSTITUTE DIAGNOSTICS,
                                        a California corporation


                                        DPD HOLDINGS, INC.,
                                        a Delaware corporation


                                        DIAGNOSTICS REFERENCE SERVICES INC.,
                                        a Maryland corporation






                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement


                                        AMERICAN MEDICAL LABORATORIES,
                                        INCORPORATED,
                                        a Delaware corporation


                                        AML INC.,
                                        a Delaware corporation


                                        QUEST DIAGNOSTICS INCORPORATED (NV),
                                        a Nevada corporation


                                        MEDICAL LABORATORIES CORPORATION
                                        d/b/a American Medical Laboratories,
                                        a Virginia corporation


                                        QUEST DIAGNOSTICS LLC,
                                        an Illinois limited liability company


                                        QUEST DIAGNOSTICS LLC,
                                        a Connecticut limited liability company


                                        QUEST DIAGNOSTICS LLC,
                                        a Massachusetts limited liability
                                        company


                                        APL PROPERTIES, LLC,
                                        a Nevada limited liability company


                                        By:
                                            ------------------------------------
                                        Name: Joseph P. Manory
                                        Title: Vice President and Treasurer


                                        PATHOLOGY BUILDING PARTNERSHIP,
                                        a Delaware general partnership


                                        By: Quest Diagnostics Incorporated, a
                                               Maryland corporation, its general
                                               partner


                                            By:
                                                --------------------------------
                                            Name: Joseph P. Manory
                                            Title: Vice President and Treasurer





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

LENDERS:

                                        BANK OF AMERICA, N.A.,
                                        individually  in its  capacity  as a
                                        Lender  and in  its  capacity  as
                                        Administrative Agent


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        ALLFIRST BANK


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        BANK HAPOALIM B.M.


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


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        THE GOVERNOR & COMPANY OF THE BANK OF
                                        IRELAND


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


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        BANK LEUMI USA


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        THE BANK OF NEW YORK


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        BANK ONE, NA (MAIN OFFICE CHICAGO)


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        BAYERISCHE HYPO- UND VEREINSBANK AG,
                                        NEW YORK BRANCH


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


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        BNP PARIBAS


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


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        CHANG HWA COMMERCIAL BANK, LTD.,
                                        NEW YORK BRANCH


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        CHINATRUST COMMERCIAL BANK, LTD.,
                                        NEW YORK BRANCH


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        CREDIT LYONNAIS NEW YORK BRANCH


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        DEUTSCHE BANK AG, NEW YORK BRANCH


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


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        E. SUN COMMERCIAL BANK, LTD.,
                                        LOS ANGELES BRANCH


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        FLEET NATIONAL BANK


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        GENERAL ELECTRIC CAPITAL CORPORATION


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        KEY CORPORATE CAPITAL INC.


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        LASALLE BANK NATIONAL ASSOCIATION


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        MERRILL LYNCH CAPITAL CORPORATION


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        MIZUHO CORPORATE BANK, LTD.


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        NATIONAL CITY BANK


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        THE NORINCHUKIN BANK, NEW YORK BRANCH


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        PB CAPITAL CORPORATION


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        PNC BANK, NATIONAL ASSOCIATION


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        SUMITOMO MITSUI BANKING CORPORATION


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        SUNTRUST BANK


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        UNION BANK OF CALIFORNIA, N.A.


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





                                Signature Page to
                               First Amendment to
                 Quest Diagnostics Incorporated Credit Agreement

                                        WACHOVIA BANK, NATIONAL ASSOCIATION


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