Exhibit 4.1

                     AMENDMENT NO. 3 TO THE RIGHTS AGREEMENT

     THIS AMENDMENT NO. 3 TO THE RIGHTS AGREEMENT, dated as of August 8, 2005,
is made between LabOne, Inc., a Missouri corporation (the "Company"), and
American Stock Transfer & Trust Company (the "Rights Agent").

                               W I T N E S S E T H

     WHEREAS, on February 11, 2000, the Company and the Rights Agent entered
into a Rights Agreement (as amended, the "Rights Agreement") to provide certain
Rights to holders of Common Stock;

     WHEREAS, on August 31, 2001, the Company and the Rights Agent entered into
Amendment No. 1 to the Rights Agreement, and on April 20, 2005, the Company and
the Rights Agent entered into Amendment No. 2 to the Rights Agreement;

     WHEREAS, the Company intends to enter into an Agreement and Plan of Merger
(the "Merger Agreement") with Quest Diagnostics Incorporated ("Quest") and
Fountain, Inc., a Missouri corporation and wholly-owned subsidiary of Quest,
which provides for, among other things, the merger of Merger Sub with and into
the Company (the "Merger"), subject to shareholder and regulatory approval and
other terms and conditions;

     WHEREAS, pursuant to Section 27 of the Rights Agreement, the Company and
the Rights Agent may from time to time supplement or amend the Rights Agreement
in accordance with the provisions of Section 27 thereof; and

     WHEREAS, the Board of Directors of the Company has determined that it is
in the best interests of the Company and its shareholders and consistent with
the objectives of the Board of Directors in adopting the Rights Agreement to
amend the Rights Agreement to except the Merger Agreement and the actions and
transactions contemplated thereby and effected in connection therewith from the
Rights Agreement;

     NOW, THEREFORE, in consideration of the premises and the mutual agreements
herein set forth, the parties hereby agree as follows:

1.   Subsection (a) of Section 1 is hereby amended by adding the following at
the end of subsection (a) of Section 1:

     Notwithstanding the foregoing or any provision to the contrary in
     this  Agreement,  none  of  Quest  Diagnostics  Incorporated,   a
     Delaware  corporation  ("Quest")  or  any  of  its  Subsidiaries,
     Affiliates  or  Associates,  shall be deemed  to be an  Acquiring
     Person  by  virtue  of  the  approval,   execution,  delivery  or
     performance  of the  Agreement  and Plan of  Merger,  dated as of
     August 8, 2005 (as the same may be amended from time to time, the
     "Merger  Agreement"),  by and  among  Quest,  Fountain,  Inc.,  a
     Missouri   corporation  and  wholly-owned   subsidiary  of  Quest
     ("Merger Sub") and the Company, or the


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     consummation  of  any  of the  transactions  contemplated  by the
     Merger Agreement,  including,  without limitation,  the merger of
     Merger  Sub  with  and into the  Company  (the  "Merger")  or the
     announcement of any of the foregoing transactions.

2.   The definition of "Section 13 Event" in Section 1(ii) of the Rights
Agreement is hereby amended by adding the following sentence at the end thereof:

     Notwithstanding  anything in this  Agreement to the  contrary,  a
     Section  13 Event  shall not be deemed  to have  occurred  as the
     result of the approval, execution, delivery or performance of the
     Merger   Agreement  or  the   consummation  of  the  transactions
     contemplated   by  the  Merger   Agreement,   including   without
     limitation,  the  Merger,  or  the  announcement  of  any  of the
     foregoing transactions.

3.   The definition of "Stock Acquisition Date" in Section 1(kk) of the Rights
Agreement is hereby amended by adding the following sentence at the end thereof:

     Notwithstanding  anything in this  Agreement to the  contrary,  a
     Stock  Acquisition Date shall not be deemed to have occurred as a
     result of the approval, execution, delivery or performance of the
     Merger   Agreement  or  the   consummation  of  the  transactions
     contemplated   by  the  Merger   Agreement,   including   without
     limitation,  the  Merger,  or  the  announcement  of  any  of the
     foregoing transactions.

4.   The definition of "Triggering Event" in Section 1(pp) of the Rights
Agreement is hereby amended by adding the following sentence at the end thereof:

     Notwithstanding  anything in this  Agreement to the  contrary,  a
     Triggering  Event  shall not be deemed  to have  occurred  as the
     result of the approval, execution, delivery or performance of the
     Merger   Agreement  or  the   consummation  of  the  transactions
     contemplated   by  the  Merger   Agreement,   including   without
     limitation,  the  Merger,  or  the  announcement  of  any  of the
     foregoing transactions.

5.   Section 3(a) of the Rights Agreement is hereby amended by adding the
following sentence at the end thereof:

     Notwithstanding  anything in this  Agreement to the  contrary,  a
     Distribution  Date  shall  not be deemed  to have  occurred  as a
     result of the approval, execution, delivery or performance of the
     Merger   Agreement  or  the   consummation  of  the  transactions
     contemplated   by  the  Merger   Agreement,   including   without
     limitation,  the  Merger,  or  the  announcement  of  any  of the
     foregoing transactions."

6.   Section 11 of the Rights Agreement is hereby amended by adding the
following sentence at the end of Section 11(a)(ii):

     Notwithstanding  anything in this  Agreement to the  contrary,  a
     Section 11(a)(ii) Event shall not be deemed to have occurred as a
     result of the approval, execution, delivery or performance of the
     Merger   Agreement  or  the   consummation  of  the  transactions
     contemplated   by  the  Merger   Agreement,   including   without
     limitation,  the  Merger,  or  the  announcement  of  any  of the
     foregoing transactions.

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7.   Section 30 of the Rights Agreement is hereby amended to add the following
sentence at the end thereof:

     Nothing in this  Agreement  shall be construed to give any holder
     of  Rights  (and,  prior  to the  Distribution  Date,  registered
     holders  of the  Common  Stock) or any other  Person any legal or
     equitable  rights,  remedies,  or claims under this  Agreement by
     virtue of the approval, execution, delivery or performance of the
     Merger   Agreement  or  the   consummation  of  the  transactions
     contemplated   by  the  Merger   Agreement,   including   without
     limitation,  the  Merger,  or  the  announcement  of  any  of the
     foregoing transactions.

8.   A new Section 35 of the Rights Agreement is hereby added, reading in its
entirety as follows:

     This Agreement and the Rights  established  hereby will terminate
     in all  respects  immediately  prior  to the  Effective  Time (as
     defined in the Merger Agreement).

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment No. 3 to
the Rights Agreement to be duly executed as of the day and year first above
written.




                               LabOne, Inc.


                               By:/s/ Joe Benage
                                  ---------------------------------
                                  Name: Joe Benage
                                  Title: Executive Vice President and
                                         General Counsel



                               American Stock Transfer & Trust Company


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