Exhibit 4.6

                     AMENDMENT NO. 1 TO THE RIGHTS AGREEMENT

     THIS AMENDMENT NO. 1 TO THE RIGHTS AGREEMENT, dated as of August 31, 2001,
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 (the "Rights Agreement") to provide certain Rights to
holders of Common Stock; and

     WHEREAS, the parties hereto desire to amend 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 deleted in its entirety, and the
following new subsection (a) is hereby inserted in lieu thereof:

          (a) "Acquiring Person" shall mean any Person who or which, together
     with all Affiliates and Associates of such Person, without the Prior
     Written Approval of the Company granted after the date hereof, shall be the
     Beneficial Owner of 15% or more of the shares of Common Stock then
     outstanding, other than as a result of a Qualifying Offer, whether or not
     such Person together with all Affiliates and Associates of such Person
     continues to be the Beneficial Owner of 15% or more of such shares.
     Notwithstanding the foregoing,

               (i) the term "Acquiring Person" shall not include any Exempt
     Person (as hereinafter defined),

               (ii) a Person shall not become an Acquiring Person solely as a
     result of a reduction in the number of shares of Common Stock outstanding
     due to the repurchase of shares of Common Stock by the Company, unless and
     until such Person (together with all Affiliates and Associates of such
     Person) shall purchase or otherwise become the Beneficial Owner of
     additional shares of Common Stock, other than pursuant to a Qualifying
     Offer or with the Prior Written Approval of the Company,

               (iii) the term "Acquiring Person" shall not include any of the
     Grant Family Members, acting individually or as a group, unless and until
     such Person or Persons (together with all Affiliates and Associates of such
     Person or Persons) shall become (other than pursuant to a Qualifying Offer
     or with the Prior Written Approval of the Company) the Beneficial Owners of
     20% or more of the shares of Common Stock then outstanding, provided that
     such Person or Persons or Affiliates or Associates shall not be deemed the
     Beneficial Owners of shares of Common Stock or other securities acquired on
     or after the


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     Rights Dividend Declaration Date pursuant to any employee or director
     benefit plan of the Company or any Subsidiary of the Company;

               (iv) the term "Acquiring Person" shall not include Welsh, Carson,
     Anderson & Stowe, IX, L.P. ("WCAS"), any general partner of WCAS, any
     member of the general partner of WCAS (collectively the "WCAS Parties") or
     any Controlled Entity, only so long as the WCAS Parties comply with Section
     6.03 of that certain Securities Purchase Agreement dated August 31, 2001
     among the Company, WCAS and the other purchasers named on Schedule I
     thereto ("Securities Purchase Agreement");

               (v) notwithstanding any other provision hereof to the contrary, a
     Person shall not be deemed to be an Acquiring Person if, within ten
     Business Days after the Board of Directors is given written notice that
     such Person has become an Acquiring Person, the Board of Directors
     determines in good faith that such Person who would otherwise be an
     "Acquiring Person" has become such inadvertently and the Board of Directors
     provides such Person a period not to exceed thirty days to divest a
     sufficient number of securities so that such Person would no longer be an
     Acquiring Person, as defined in the foregoing provisions of this paragraph
     (a), and such Person has so divested prior to the end of such period.

               Notwithstanding anything in this Agreement to the contrary, the
     term "then outstanding," when used with reference to a Person's beneficial
     ownership of securities of the Company, shall mean the number of such
     securities then issued and outstanding together with the number of such
     securities not then actually issued and outstanding which such Person would
     be deemed to beneficially own hereunder.

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

          Notwithstanding the foregoing, (i) no Affiliate or Associate of any of
     the WCAS Parties that is not a Controlled Entity shall be deemed to be the
     Beneficial Owner of shares of Common Stock beneficially owned by the WCAS
     Parties solely by reason of such Person being an Affiliate or Associate of
     any of the WCAS Parties and (ii) none of the Grant Family Members, on the
     one hand, and WCAS Parties, on the other hand, shall be deemed to
     beneficially own the shares of Common Stock beneficially owned by the other
     as a result of (A) the execution, delivery and performance of the Voting
     Agreement dated August 31, 2001 between certain WCAS Parties and certain
     Grant Family Members or (B) compliance by the Company and any of the WCAS
     Parties with Section 6.02 of the Securities Purchase Agreement.

     3. Subsection (y) of Section 1 is hereby deleted in its entirety, and the
following new subsection (y) is hereby inserted in lieu thereof:

          (y) "Prior Written Approval" shall mean the prior express written
     consent of the Company to any Person becoming an Acquiring Person, executed
     on behalf of the Company by a duly authorized officer of the Company
     following express approval by action of the

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     Board of Directors (and approval of a majority of the Non-WCAS Directors
     with respect to WCAS or any Controlled Entity becoming an Acquiring Person
     and approval of a majority of the WCAS Directors with respect to any Grant
     Family Member becoming an Acquiring Person), provided that all conditions
     precedent and subsequent established by the Board of Directors (and not
     waived by the Board of Directors prior to violation of any such condition)
     in connection with such approval shall be satisfied.

     4. Section 1 is hereby amended to include the following new subsection
after subsection (pp):

          (qq) "Controlled Entity" shall mean any entity in which any one or
     more of the WCAS Parties owns a majority of the voting shares or securities
     or has the ability (whether through the ownership of voting securities,
     contract or otherwise) to elect a majority of the board of directors or
     similar governing body or of which any one or more of the WCAS Parties has
     the authority to control or direct investment decisions.

     5. Section 1 is hereby amended to include the following new subsection
after subsection (qq):

          (rr) "WCAS Director" shall mean each member of the Board of Directors
     who is: (i) directly elected by the Series B-1 Preferred Stock and/or
     Series C-1 Preferred Stock of the Company or (ii) nominated or designated
     for nomination by the Purchaser Representative (as defined in such
     agreement) pursuant to Section 6.02 of the Securities Purchase Agreement
     dated August 31, 2001 among the Company, WCAS and the other purchasers
     named on Schedule I thereto.

     6. Section 1 is hereby amended to include the following new subsection
after subsection (rr):

          (ss) "Non-WCAS Director" shall mean each member of the Board of
     Directors who is not a WCAS Director.

     7. Section 27 is hereby deleted in its entirety, and the following new
Section 27 is hereby inserted in lieu thereof:

          At any time and from time to time prior to the close of business on
     the tenth Business Day after the Stock Acquisition Date, the Board of
     Directors, upon vote of a majority of the Board of Directors then in
     office, may in its sole and absolute discretion amend or supplement this
     Agreement without the approval of any holders of Rights; provided that any
     amendment that deletes, modifies, supersedes or otherwise affects Sections
     1(a)(iv), 1(y), 1(qq), 1(rr), 1(ss) or 27 shall also require the approval
     of a majority of the Non-WCAS Directors, and provided, further that any
     amendment that deletes, modifies, supersedes or otherwise affects Sections
     1(a)(iii), 1(y), 1(rr), 1(ss) or 27 shall also require the approval of a
     majority of the WCAS Directors. At any time and from time to time after the
     close of business on the tenth Business Day after the Stock Acquisition
     Date, the Board of Directors, upon vote of a majority of the Board of
     Directors then in office, may

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     supplement or amend this Agreement without the approval of any holders of
     the Rights, provided that no such supplement or amendment adversely affects
     the interests of the holders of Rights as such (other than an Acquiring
     Person or an Affiliate or Associate of an Acquiring Person). Upon the
     delivery of a certificate from an appropriate officer of the Company which
     states that the proposed supplement or amendment is in compliance with the
     terms of this Section 27, the Rights Agent shall execute such supplement or
     amendment; provided, however, that the Rights Agent may, but shall not be
     obligated to, enter into any such supplement or amendment which adversely
     affects the Rights Agent's own rights, duties or immunities under this
     Agreement.

     IN WITNESS WHEREOF, the parties hereto have caused this Amendment No.1 to
the Rights Agreement to be duly executed as of the day and year first above
written.


                            LABONE, INC.


                            By:  /s/ W. Thomas Grant II
                               -----------------------------------------
                               Name:   W. Thomas Grant II
                               Title:  Chairman of the Board, President
                                       and Chief Executive Officer



                            AMERICAN STOCK TRANSFER & TRUST COMPANY


                            By:  /s/ Herbert J. Lemmer
                               ----------------------------------------
                               Name:  Herbert J. Lemmer
                               Title: Vice President


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