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                                                                     EXHIBIT 4.4

                       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 Company 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 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 sentence in Section 21 that begins on line 24 of page 52 with
            "Any successor rights agent. . . ." and ends on line 9 of page 53
            with ". . . combined capital and surplus of at least $50,000,000" is
            hereby deleted and replaced as follows:

            Any successor Rights Agent, whether appointed by the Company or by
            such a court, shall be: (a) a corporation, limited liability company
            or trust company (or


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            similar form of entity under 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, limited liability company or entity
            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 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.    Section 20(c) of the Rights Agreement is hereby deleted and replaced
            as follows:

            The Rights Agent shall be liable hereunder to the Company and any
            other Person only for its own gross negligence or willful
            misconduct.

      7.    The sentence in Section 18 that begins on line 7 of page 45 with
            "The Company also agrees. . . ." and ends on line 14 of page 45 with
            ". . . liability in the premises" is hereby deleted and replaced as
            follows:

            The Company also agrees to indemnify and hold harmless Computershare
            and each member, director, officer, employee, and affiliate of
            Computershare,


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            (collectively, the "Indemnified Parties") against any and all
            actions, claims, demands, losses, damages, liabilities, costs and
            expenses of any kind or nature whatsoever (including without
            limitation, reasonable attorneys' and consultants' fees, costs and
            expenses) incurred by or asserted against any of the Indemnified
            Parties from and after the date hereof, relating to, or in
            connection with Computershare's provision of services under the
            Rights Agreement (including, without limitation, responding to any
            demand or claim of liability in the premises) or any breach by the
            Company of any term or condition of the Rights Agreement; provided,
            however, that no Indemnified Party shall have the right to be
            indemnified hereunder for any liability finally determined by a
            court of competent jurisdiction, subject to no further appeal, to
            have resulted solely from the gross negligence or willful misconduct
            of such Indemnified Party.

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

      9.    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.

      10.   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:
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Name: Leo C. Farrenkopf, Jr.              Name:
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Title: Vice President and Secretary       Title:
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HARRIS TRUST AND SAVINGS BANK
Rights Agent


By:
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Title:
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