Document:

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                                                                   Exhibit 10.30

                       AMENDMENT NO. 3 TO RIGHTS AGREEMENT

         THIS AMENDMENT (this "Amendment") effective as of the 18th day of
October, 2000, amends and modifies, at the Company's direction, a certain Rights
Agreement dated as of December 31, 1996, as previously amended (the "Rights
Agreement") between Quest Diagnostics Incorporated (the "Company") and Harris
Trust and Savings Bank, as Rights Agent. All terms defined in the Rights
Agreement shall have the same meanings in this Amendment unless otherwise
defined.

         WHEREAS, Quest Diagnostics Incorporated (the "Corporation") has
previously appointed Harris Trust and Savings Bank or an affiliate thereof
("Harris") as Rights Agent under the Rights Agreement; and

         WHEREAS, Section 21 of the Rights Agreement headed "Change of Rights
Agent" provides for the appointment of a successor Rights Agent, and sets forth
specified requirements for any such successor Rights Agent; and

         Whereas, Harris wishes to terminate its appointment, as of the
Effective Date stated below, as Rights Agent in light of the transfer of certain
of its operations to Computershare Investor Services, L.L.C., a Delaware limited
liability company, together with its affiliates, ("Computershare"); and

         WHEREAS, the Corporation wishes to appoint Computershare as successor
Rights Agent and Computershare consents to such appointment; and

         WHEREAS, effective December 8, 1999, the Rights Agreement was amended
to increase the exercise price of a Right under Section 7(b) of the Right
Agreement from $35 to $125; and

         WHEREAS, on October 18, 2000, the Board of Directors of the Company
adopted a resolution approving the amendment of the Rights Agreement to increase
the exercise price of a Right under Section 7(b) of the Rights Agreement to from
$125 to $500;

         NOW, THEREFORE, in consideration of the premises, the parties hereto
agree as follows:

          1.   All terms not defined herein have the meanings set forth in the
               Rights Agreement.

          2.   The fifth sentence of Section 21 of the Rights Agreement
               beginning with "Any successor Rights Agent" and ending with
               "surplus of at least $50 million," shall be deleted and replaced
               with the following:

                    Any successor Rights Agent, whether appointed by the Company
                    or by such a court, shall be: (a) a corporation or trust
                    company (or similar form of entity under

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                    the laws of any state of the United States or a foreign
                    jurisdiction) authorized to conduct business under the laws
                    of the United States or any state of the United States,
                    which is authorized under such laws to exercise corporate
                    trust, fiduciary or stockholder services powers and is
                    subject to supervision or examination by a federal or state
                    authority and which has, at the time of its appointment as
                    Rights Agent, a combined capital and surplus of at least
                    $10,000,000; or (b) an Affiliate controlled by a corporation
                    described in clause (a) of this sentence.

          3.   Computershare Investor Services LLC ("Computershare") is hereby
               appointed as Successor Rights Agent under the above Rights
               Agreement, succeeding Harris, effective as of the date of this
               Amendment ("Effective Date"), to act in accordance with and
               pursuant to the terms and conditions of the Rights Agreement.

          4.   Computershare's execution of this Agreement shall constitute the
               acceptance by the Computershare of the agency herein conferred,
               and shall evidence its agreement to carry out and perform its
               duties under the Rights Agreement in accordance with the
               provisions thereof, as previously and hereby amended.

          5.   Computershare and its affiliates will be entitled to rely and act
               upon any written orders or directions regarding the issuance and
               delivery of certificates for the above described shares signed by
               the Secretary or any Assistant Secretary of the Corporation AND
               by one of the following officers:

                           Chief Executive Officer
                           President
                           Chief Operating Officer
                           Chief Financial Officer
                           Treasurer
                           Corporate Controller
                           General Counsel

               or any list, instrument, order, paper, stock certificate,
               signature or guarantee believed by Computershare and its
               affiliates in good faith to be genuine and to have been signed,
               countersigned or executed by any such authorized officers;

          6.   The Corporation will indemnify and hold Computershare and its
               affiliates harmless from all liability, damages, costs, charges
               and expenses, including fees and expenses of counsel, which any
               of them may incur for any action taken or omitted to be taken in
               their reliance as aforesaid or otherwise for any action taken or
               omitted to be taken by them in good faith, with due diligence and
               without negligence.

          7.   Section 7(b) of the Rights Agreement is hereby deleted and
               replaced as follows:

               (b)  The Purchase Price for each one one-hundredth of a Preferred
                    Share purchasable pursuant to the exercise of a Right shall
                    be Five Hundred Dollars ($500.00), and shall be subject to
                    adjustment from time to time as provided in Section 11 or 13
                    hereof and shall be payable in

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                    lawful money of the United States of America in accordance
                    with paragraph (c) below.

          8.   This Amendment shall be deemed to be a contract made under the
               laws of the State of Delaware and for all purposes shall be
               governed by and construed in accordance with the laws of such
               State applicable to contracts to be made and performed entirely
               within such State.

          9.   Except as expressly amended hereby, all the terms and conditions
               of the Rights Agreement, as previously amended, shall remain in
               full force and effect.

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

QUEST DIAGNOSTICS INCORPORATED              COMPUTERSHARE INVESTOR
                                            SERVICES LLC, Successor Rights Agent

By:                                         By:
   ----------------------------------          ---------------------------------
Name: LEO C. FARRENKOPF, JR.                Name:
     --------------------------------            -------------------------------
Title: VICE PRESIDENT AND SECRETARY         Title:
       -----------------------------              ------------------------------

HARRIS TRUST AND SAVINGS BANK
Rights Agent

By:
   ----------------------------------

Title:
      -------------------------------<PAGE>

                                                                   EXHIBIT 10.31

                                 AMENDMENT NO. 1

         AMENDMENT NO. 1 ("AMENDMENT NO. 1") dated as of December 17, 1999 to
the Credit Agreement dated as of August 16, 1999 (as amended, amended and
restated or otherwise modified and supplemented and in effect from time to time,
the "CREDIT AGREEMENT") among Quest Diagnostics Incorporated (the "BORROWER");
the guarantors party thereto (the "GUARANTORS"); certain lenders (the
"LENDERS"); Merrill Lynch & Co., Merrill Lynch, Pierce, Fenner & Smith
Incorporated ("MERRILL LYNCH"), as joint lead arranger; Banc of America
Securities LLC, as joint lead arranger (in such capacity, together with its
successors and Merrill Lynch together with its successors in its capacity as
joint lead arranger, the "JOINT LEAD ARRANGERS"); Bank of America, N.A., as
administrative agent ("ADMINISTRATIVE AGENT"); Wachovia Bank, N.A. ("WACHOVIA"),
as co-documentation agent; The Bank of New York, as co-documentation agent (in
such capacity, together with Wachovia as co-documentation agent, the
"CO-DOCUMENTATION AGENTS"); and Merrill Lynch & Co., Merrill Lynch, Pierce,
Fenner & Smith Incorporated, as syndication agent (in such capacity, together
with its successors in such capacity, the "SYNDICATION AGENT"). Capitalized
terms not otherwise defined in this Amendment No. 1 have the same meaning
assigned to such terms in the Credit Agreement.

                              W I T N E S S E T H :

         WHEREAS, pursuant to Section 12.04 of the Credit Agreement, the
Obligors and the Majority Lenders hereby agree to amend or waive certain
provisions of the Credit Agreement as set forth herein;

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

         SECTION ONE - AMENDMENT. The Lenders and Agents amend, effective as of
the date hereof and subject to the satisfaction of the conditions in Section Two
hereof the following:

         (a) Section 9.08(A)(c) is amended by inserting "(i)" after
"Indebtedness and Contingent Obligations of" at the be

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                                      -2-

ginning of this subsection and by adding the following immediately after the
end of this subsection before the semicolon:

               "and (ii) any Company to any Receivables Co. in connection with
               any Permitted Receivables Transaction; PROVIDED, HOWEVER, that
               such Indebtedness and Contingent Obligations shall be
               subordinated to the Obligations and on terms and conditions
               acceptable to Joint Lead Arrangers"

         (b) Section 9.08(A)(i) is amended by adding the following immediately
prior to the proviso thereto:

               "(and, notwithstanding any provision of any Security Document to
               the contrary, any Indebtedness incurred under this Section
               9.08(A)(i)(ii) need not be pledged to the Creditors nor do the
               Creditors have any security interest therein pursuant to the
               Credit Documents)"

         (c) Section 9.21 is amended by adding the following at the end thereof
as a new paragraph:

               "Notwithstanding any provision to the contrary, this Section 9.21
               does not apply to any Indebtedness incurred pursuant to Section
               9.08(A)(c) or Section 9.08(A)(i)(ii)"

         SECTION TWO - CONDITIONS TO EFFECTIVENESS. This Amendment No. 1 shall
become effective as of the date first above written when, and only when,
Administrative Agent shall have received counterparts of this Amendment No. 1
executed by each Obligor and the Majority Lenders or, as to any of the Lenders,
advice satisfactory to Administrative Agent that such Lender has executed this
Amendment No. 1.

         SECTION THREE - REPRESENTATIONS AND WARRANTIES. In order to induce the
Lenders and Agents to enter into this Amendment No. 1, each Obligor represents
and warrants to each of the Lenders and Agents that after giving effect to this
Amendment No. 1, (i) no Default or Event of Default has occurred and is
continuing; and (ii) all of the representations

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                                      -3-

and warranties of Borrower and the other Obligors in the Credit Agreement, after
giving effect to this Amendment No. 1, are true and complete in all material
respects on and as of the date hereof as if made on the date hereof (or, if any
such representation or warranty is expressly stated to have been made as of a
specific date, as of such specific date).

         SECTION FOUR - REFERENCE TO AND EFFECT ON THE CREDIT AGREEMENT AND THE
SECURITY AGREEMENT. On and after the effectiveness of this Amendment No. 1, each
reference in the Credit Agreement or the Security Agreement to "this Agreement",
"hereunder", "hereof" or words of like import referring to the Credit Agreement
or the Security Agreement, respectively, and each reference in each of the other
Credit Documents to "the Credit Agreement", "the Security Agreement",
"thereunder", "thereof" or words of like import referring to the Credit
Agreement or the Security Agreement, shall mean and be a reference to the Credit
Agreement or the Security Agreement, respectively, as amended by this Amendment
No. 1. The Credit Agreement, the Security Agreement, and each of the other
Credit Documents, as specifically amended by this Amendment No. 1, are and shall
continue to be in full force and effect and are hereby in all respects ratified
and confirmed. Without limiting the generality of the foregoing, the Security
Documents and all of the Collateral described therein do and shall continue to
secure the payment of all Obligations of the Obligors under the Credit
Documents, in each case as amended by this Amendment No. 1. The execution,
delivery and effectiveness of this Amendment No. 1 shall not, except as
expressly provided herein, operate as a waiver of any right, power or remedy of
any Lender or any Agent under any of the Credit Documents, nor constitute a
waiver of any provision of any of the Credit Documents.

         SECTION FIVE - COSTS, EXPENSES AND TAXES. The Obligors agree to pay all
reasonable costs and expenses of Administrative Agent in connection with the
preparation, execution and delivery of this Amendment No. 1 and the other
instruments and documents to be delivered hereunder, if any (including, without
limitation, the reasonable fees and expenses of Cahill Gordon & Reindel) in
accordance with the terms of Section 12.03 of the Credit Agreement.

         SECTION SIX - EXECUTION IN COUNTERPARTS. This Amendment No. 1 may be
executed in any number of counterparts and by different parties hereto in
separate counterparts, each of which when so executed shall be deemed to be an
original and all of which taken together shall constitute but one and the same
agreement. Delivery of an executed counterpart of a sig-

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                                      -4-

nature page to this Amendment No. 1 by telecopier shall be effective as delivery
of a manually executed counterpart of this Amendment No. 1.

         SECTION SEVEN - GOVERNING LAW. This Amendment No. 1 shall be governed
by, and construed in accordance with, the laws of the State of New York (without
giving effect to any provisions thereof relating to conflicts of law).

                  [Remainder of Page Intentionally Left Blank]

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                                      S-1

                  IN WITNESS WHEREOF, the parties hereto have caused this
Amendment No. 1 to be executed by their respective officers thereunto duly
authorized, as of the date first above written.

                                        QUEST DIAGNOSTICS INCORPORATED

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

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                                      S-2

                                 GUARANTORS:

                                    SBCL, Inc. (DE)
                                    SmithKline Beecham Clinical
                                       Laboratories, Inc. (DE)
                                    Quest Diagnostics Incorporated (CA)
                                    Quest Holdings Incorporated (MD)
                                    Quest Diagnostics Incorporated (MD)
                                    Quest Holdings Incorporated (MI)
                                    Quest Diagnostics LLC (IL)
                                    Quest Diagnostics Incorporated (MI)
                                    Quest Diagnostics Incorporated (CT)
                                    Quest Diagnostics Incorporated (MA)
                                    Quest Diagnostics of Pennsylvania
                                       Inc. (DE)
                                    Quest Diagnostics Incorporated (OH)
                                    MetWest Inc. (DE)
                                    Nichols Institute Diagnostics (CA)
                                    DPD Holdings, Inc. (DE)
                                    Diagnostics Reference Services Inc.
                                       (MD)
                                    Laboratory Holding Incorporated (MA)
                                    Quest MRL Inc. (DE)

                                    Each as a Guarantor and Pledgor

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

                                    QUEST DIAGNOSTICS INVESTMENTS
                                    INCORPORATED

                                    QUEST DIAGNOSTICS FINANCE
                                    INCORPORATED

                                    Each as a Guarantor and Pledgor

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

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                                      S-3

                                    PATHOLOGY BUILDING PARTNERSHIP, by
                                    Quest Diagnostics Incorporated
                                      (MD), as General Partner

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

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                                      S-4

                                  AGENTS:

                                    MERRILL LYNCH & CO.
                                    MERRILL LYNCH, PIERCE, FENNER &
                                       SMITH INCORPORATED,
                                    as Joint Lead Arranger and
                                    Syndication Agent

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

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                                      S-5

                                    BANC OF AMERICA SECURITIES LLC,
                                    as Joint Lead Arranger

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

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                                      S-6

                                    BANK OF AMERICA, N.A.,
                                    as Administrative Agent

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

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                                      S-7

                                    WACHOVIA BANK, N.A.,
                                    as Co-Documentation Agent

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

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                                      S-8

                                    THE BANK OF NEW YORK,
                                    as Co-Documentation Agent

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

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                                      S-9

                                    ------------------------------------,
                                    as a Lender (please type)

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

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