<PAGE>

                                                                    EXHIBIT 99.4

                       LETTER OF ELECTION AND TRANSMITTAL
                        TO TENDER SHARES OF COMMON STOCK

                                       OF

                               UNILAB CORPORATION
                                       TO

                      QUEST DIAGNOSTICS NEWCO INCORPORATED
                          A WHOLLY OWNED SUBSIDIARY OF

                         QUEST DIAGNOSTICS INCORPORATED
                 PURSUANT TO THE PROSPECTUS DATED MAY 15, 2002

  THE OFFER AND WITHDRAWAL RIGHTS WILL EXPIRE AT 12:00 MIDNIGHT, NEW YORK CITY
 TIME, ON MONDAY, JUNE 17, 2002, UNLESS THE OFFER IS EXTENDED. SHARES TENDERED
 PURSUANT TO THIS OFFER MAY BE WITHDRAWN AT ANY TIME PRIOR TO THE EXPIRATION OF
                                   THE OFFER.

                          The Offer Exchange Agent is:
                    COMPUTERSHARE TRUST COMPANY OF NEW YORK

<Table>
<S>                                 <C>                                 <C>
             By Mail:                         By Facsimile:               By Overnight or Hand Delivery:



Computershare Trust Company of New  Computershare Trust Company of New  Computershare Trust Company of New
               York                                York                                York
       Wall Street Station             By Facsimile: (212) 701-7636             Wall Street Plaza
          P.O. Box 1010                 Telephone: (212) 701-7624           88 Pine Street, 19th Floor
  New York, New York 10268-1010                                              New York, New York 10005
</Table>

     Delivery of this Letter of Election and Transmittal to an address or
transmission via a facsimile number other than as set forth above will not
constitute a valid delivery to the Offer Exchange Agent. You must sign this
Letter of Election and Transmittal where indicated below, with signature
guarantee if required, and complete the Substitute Form W-9 provided below.

     The instructions contained within this Letter of Election and Transmittal
should be read carefully before this Letter of Election and Transmittal is
completed.
--------------------------------------------------------------------------------
                         DESCRIPTION OF SHARES TENDERED

<Table>
<Caption>
---------------------------------------------------------------------------------------------------------------------------------
      NAME(S) AND ADDRESS(ES) OF REGISTERED HOLDER(S)
       (PLEASE FILL IN, IF BLANK, EXACTLY AS NAME(S)                      SHARE CERTIFICATE(S) AND SHARE(S) TENDERED
             APPEAR(S) ON SHARE CERTIFICATE(S))                             (ATTACH ADDITIONAL LIST, IF NECESSARY)
---------------------------------------------------------------------------------------------------------------------------------
                                                                                       TOTAL NUMBER OF
                                                               SHARE CERTIFICATE     SHARES EVIDENCED BY      NUMBER OF SHARES
                                                                   NUMBER(S)*       SHARE CERTIFICATE(S)*        TENDERED**
<S>                                                          <C>                    <C>                    <C>
                                                               ---------------------------------------------------------------

                                                               ---------------------------------------------------------------

                                                               ---------------------------------------------------------------

                                                               ---------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------------------------
                                                                  TOTAL SHARES
---------------------------------------------------------------------------------------------------------------------------------
</Table>

  * Need not be completed by stockholders delivering Shares by book-entry
 transfer.

 ** Unless otherwise indicated, it will be assumed that all Shares evidenced by
    each Share Certificate delivered to the Offer Exchange Agent are being
    tendered hereby. See Instruction 4.

 [ ]  CHECK HERE IF CERTIFICATES HAVE BEEN LOST, DESTROYED OR STOLEN. SEE
      INSTRUCTION 11.
--------------------------------------------------------------------------------
--------------------------------------------------------------------------------
<PAGE>

     This Letter of Election and Transmittal is to be used by stockholders of
Unilab Corporation (the "Company") if certificates evidencing Shares (as defined
below) are to be forwarded herewith or, unless an agent's message (as defined in
Instruction 2 below) is utilized, if delivery of Shares is to be made by
book-entry transfer to an account maintained by the Offer Exchange Agent at the
Book-Entry Transfer Facility (as defined in and pursuant to the procedures set
forth under "The Offer -- Procedure for Tendering and Electing" in the
Prospectus (as defined below)).

     Stockholders whose certificates for Shares are not immediately available or
who cannot deliver their certificates and all other documents required hereby to
the Offer Exchange Agent prior to the expiration date (as defined in the
Prospectus, dated May 15, 2002 (the "Prospectus")), or who cannot comply with
the book-entry transfer procedures on a timely basis, may nevertheless tender
their Shares according to the guaranteed delivery procedures set forth under
"The Offer -- Procedure for Tendering and Electing -- Guaranteed Delivery" in
the Prospectus. See Instruction 2. DELIVERY OF DOCUMENTS TO A BOOK-ENTRY
TRANSFER FACILITY WILL NOT CONSTITUTE DELIVERY TO THE OFFER EXCHANGE AGENT.

                                    ELECTION

                        (See Instructions 2, 12 and 13)

Please list the total number of Shares held by you: --------------------

Number of Shares being tendered: --------------------

[ ]  CHECK HERE IF YOU ARE ELECTING TO RECEIVE CASH FOR ALL YOUR SHARES, SUBJECT
     TO PRORATION.

[ ]  CHECK HERE IF YOU ARE ELECTING TO RECEIVE QUEST DIAGNOSTICS SHARES FOR ALL
     YOUR SHARES.

[ ]  CHECK HERE TO EXCHANGE __________ SHARES FOR CASH AND THE REMAINDER FOR
     QUEST DIAGNOSTICS SHARES.

                                TENDER OF SHARES

[ ]  CHECK HERE IF SHARES ARE BEING DELIVERED BY BOOK-ENTRY TRANSFER TO THE
     OFFER EXCHANGE AGENT'S ACCOUNT AT THE BOOK-ENTRY TRANSFER FACILITY AND
     COMPLETE THE FOLLOWING:

     Name of Tendering Institution:
    ----------------------------------------------------------------------------

     Account Number:
    ----------------------------------------------------------------------------

     Transaction Code Number:
    ----------------------------------------------------------------------------

                                        2
<PAGE>

[ ]  CHECK HERE IF SHARES ARE BEING TENDERED PURSUANT TO A NOTICE OF GUARANTEED
     DELIVERY PREVIOUSLY SENT TO THE OFFER EXCHANGE AGENT AND COMPLETE THE
     FOLLOWING:

     Name(s) of Registered Holder(s):

     Window Ticket No. (if any):

     Date of Execution of Notice of Guaranteed Delivery:

     Name of Institution that Guaranteed Delivery:

     If delivery is by book-entry transfer, give the following information:

     Account Number:

     Transaction Code Number:

                    NOTE: SIGNATURES MUST BE PROVIDED BELOW.
              PLEASE READ THE ACCOMPANYING INSTRUCTIONS CAREFULLY.

Ladies and Gentlemen:

     The undersigned hereby delivers to Quest Diagnostics Newco Incorporated
("Purchaser"), a Delaware corporation and a wholly owned subsidiary of Quest
Diagnostics Incorporated, a Delaware corporation ("Quest Diagnostics"), the
above-described shares of common stock, par value $.01 per share ("Shares"), of
Unilab Corporation, a Delaware corporation (the "Company"), pursuant to
Purchaser's offer to exchange each outstanding Share for, at the election of the
holder thereof, (i) 0.3256 of a share of common stock, par value $.01 per share,
of Quest Diagnostics ("Quest Diagnostics Shares") or (ii) $26.50 in cash,
without interest, upon the terms and subject to the conditions set forth in the
Prospectus and this Letter of Election and Transmittal (which, together with any
amendments or supplements thereto, collectively constitute the "Offer"). Receipt
of the Offer is hereby acknowledged. The undersigned understands that Purchaser
reserves the right to transfer or assign, in whole or from time to time in part,
to one or more wholly owned subsidiaries, the right to purchase Shares tendered
pursuant to the Offer, but any such transfer or assignment will not relieve
Purchaser of its obligations under the Offer and will not prejudice the rights
of tendering stockholders to receive payment for Shares validly tendered and
accepted for payment in the Offer.

     The undersigned elects to have his, her or its Shares exchanged pursuant to
one or more of the following options, in the manner indicated in the "Election"
box above:

     - cash election:  the undersigned elects to exchange each of his, her or
       its tendered Shares for $26.50 in cash, without interest, subject to
       proration as described below and in the Prospectus;

     - stock election:  the undersigned elects to exchange each of his, her or
       its tendered Shares for 0.3256 of a Quest Diagnostics Share; or

     - the undersigned elects to exchange some of his, her or its tendered
       Shares for cash and elects to exchange others of his, her or its Shares
       for Quest Diagnostics Shares.

     THE AGGREGATE CASH CONSIDERATION THAT THE UNDERSIGNED MAY RECEIVE IN THE
OFFER IS SUBJECT TO A PRO RATA REDUCTION BECAUSE NOT MORE THAN 30% OF THE NUMBER
OF SHARES OUTSTANDING IMMEDIATELY PRIOR TO THE EXPIRATION OF THE OFFER, WHICH WE
REFER TO AS THE MAXIMUM CASH ELECTION NUMBER, CAN BE EXCHANGED FOR CASH. If the
maximum cash election number is exceeded, each tendered Share properly electing
to receive $26.50 in cash, without interest, will be exchanged for (a) an amount
of cash, without interest, equal to the product of (x) $26.50 and (y) a fraction
(referred to as the cash fraction), the numerator of which will be the maximum
cash election number (that is, 30% of the number of Shares outstanding
immediately prior to expiration of the Offer), and the denominator of which will
be the total number of validly tendered

                                        3
<PAGE>

and not withdrawn Shares electing to receive the cash consideration, and (b) a
number of Quest Diagnostics Shares equal to the product of (x) 0.3256 of a Quest
Diagnostics Share and (y) a fraction equal to one minus the cash fraction.

     IF THE UNDERSIGNED FAILS TO PROPERLY MAKE AN ELECTION, THE UNDERSIGNED WILL
BE DEEMED TO HAVE ELECTED TO RECEIVE QUEST DIAGNOSTICS SHARES IN EXCHANGE FOR
ALL OF THE UNDERSIGNED'S SHARES, AND WILL RECEIVE 0.3256 OF A QUEST DIAGNOSTICS
SHARE FOR EACH SHARE VALIDLY TENDERED FOR EXCHANGE.

     Upon the terms and subject to the conditions of the Offer (and, if the
Offer is extended or amended, the terms of any such extension or amendment), and
subject to, and effective upon, acceptance for payment of Shares tendered
herewith in accordance with the terms of the Offer, the undersigned hereby
sells, assigns and transfers to, or upon the order of, Purchaser all right,
title and interest in and to all Shares that are being tendered hereby (and any
and all non-cash dividends, non-cash distributions, including, without
limitation, distributions of additional Shares, and rights declared, paid or
distributed in respect of such Shares on or after the date of execution of this
Letter or Election and Transmittal (collectively, "Distributions")) and
irrevocably constitutes and appoints Computershare Trust Company of New York
(the "Offer Exchange Agent") the true and lawful agent and attorney-in-fact of
the undersigned with respect to such Shares (and all Distributions), with full
power of substitution (such power of attorney being deemed to be an irrevocable
power coupled with an interest), to (i) deliver certificates for such Shares
(and any and all Distributions) or transfer ownership of such Shares (and any
and all Distributions) on the account books maintained by the Book-Entry
Transfer Facility, together, in either case, with all accompanying evidences of
transfer and authenticity, to, or upon the order of, Purchaser, (ii) present
such Shares (and any and all Distributions) for transfer on the books of the
Company, and (iii) receive all benefits and otherwise exercise all rights of
beneficial ownership of such Shares (and any and all Distributions), all in
accordance with the terms of the Offer.

     By executing this Letter of Election and Transmittal, the undersigned
hereby irrevocably appoints Michael E. Prevoznik and Leo C. Farrenkopf, Jr., in
their respective capacities as employees of Quest Diagnostics or Purchaser, and
any individual who shall thereafter succeed to any office of Quest Diagnostics
or Purchaser held by either of them, and each of them, as the attorneys-in-fact
and proxies of the undersigned, each with full power of substitution and
resubstitution, to vote in such manner as each such attorney-in-fact and proxy
or his or her substitute shall, in his or her sole discretion, deem proper and
otherwise act (by written consent or otherwise) with respect to all Shares
tendered hereby that have been accepted for payment by Purchaser prior to the
time of such vote or other action and all Shares and other securities issued in
Distributions in respect of such Shares, which the undersigned is entitled to
vote at any meeting of stockholders of the Company (whether annual or special
and whether or not adjourned or postponed) or consent in lieu of any such
meeting or otherwise. This proxy and power of attorney is coupled with an
interest in Shares tendered hereby, is irrevocable and is granted in
consideration of, and is effective upon, the acceptance for payment of such
Shares by Purchaser in accordance with other terms of the Offer. Such acceptance
for payment shall, without further action, revoke all other proxies and powers
of attorney granted by the undersigned at any time with respect to such Shares
(and all Shares and other securities issued in Distributions in respect of such
Shares), and no subsequent proxies, powers of attorney, consents or revocations
may be given by the undersigned with respect thereto (and, if given, will not be
deemed effective). The undersigned understands that, in order for Shares or
Distributions to be deemed validly tendered, immediately upon Purchaser's
acceptance of such Shares for payment, Purchaser must be able to exercise full
voting, consent and other rights with respect to such Shares (and any and all
Distributions), including, without limitation, voting at any meeting of the
Company's stockholders then scheduled.

     The undersigned hereby represents and warrants that the undersigned has
full power and authority to tender, sell, assign and transfer Shares tendered
hereby and all Distributions, that when such Shares are accepted for payment by
Purchaser, Purchaser will acquire good, marketable and unencumbered title
thereto and to all Distributions, free and clear of all liens, restrictions,
charges and encumbrances, and that none of such Shares and Distributions will be
subject to any adverse claims. The undersigned, upon request, will execute and
deliver all additional documents deemed by the Offer Exchange Agent or Purchaser
to be necessary or desirable to complete the sale, assignment and transfer of
Shares tendered hereby and all Distributions. In addition, the undersigned will
remit and transfer promptly to the Offer Exchange Agent for the account of
Purchaser all Distributions in respect of Shares tendered hereby, accompanied by
appropriate documentation of transfer, and, pending such remittance and transfer
or appropriate assurance thereof, Purchaser shall be entitled to all rights and
privileges as owner of each such Distribution and may withhold the entire
purchase price of Shares tendered hereby, or deduct from such total
consideration, the amount or value of such Distribution as determined by
Purchaser in its sole discretion.
                                        4
<PAGE>

     The undersigned represents and warrants that the undersigned has read and
agrees to all the terms and conditions of the Offer. No authority herein
conferred or agreed to be conferred shall be affected by, and all such authority
shall survive, the death or incapacity of the undersigned. All obligations of
the undersigned hereunder shall be binding upon the heirs, personal
representatives, trustees in bankruptcy, successors and assigns of the
undersigned. Except as stated in the Offer, this tender is irrevocable.

     The undersigned understands that the valid tender of Shares pursuant to any
one of the procedures described in "The Offer -- Procedures for Tendering and
Electing" in the Prospectus and in the Instructions hereto will constitute the
undersigned's acceptance of the terms and conditions of the Offer. Purchaser's
acceptance of such Shares for payment will constitute a binding agreement
between the undersigned and Purchaser upon the terms and subject to the
conditions of the Offer (and, if the Offer is extended or amended, the terms or
conditions of any such extension or amendment). The undersigned recognizes that,
under certain circumstances set forth in the Prospectus, Purchaser may not be
required to accept for exchange any of the Shares tendered hereby.

     Unless otherwise indicated below in the box entitled "Special Payment
Instructions", please issue the Quest Diagnostics Shares, and/or a check for any
cash consideration or cash received in lieu of fractional Quest Diagnostics
Shares payable pursuant to the Offer, and return any certificates for Shares not
tendered or not accepted for exchange in the Offer, in the name(s) of the
registered holder(s) appearing under "Description of Shares Tendered".
Similarly, unless otherwise indicated below in the box entitled "Special
Delivery Instructions", please mail the Quest Diagnostics Shares and/or a check
for any cash consideration or cash received in lieu of fractional Quest
Diagnostics Shares (and any accompanying documents, as appropriate), and return
any certificates for Shares not tendered or accepted for exchange in the Offer,
to the address(es) of the registered holder(s) appearing above under
"Description of Shares Tendered" on the reverse hereof. In the event that the
boxes below entitled "Special Payment Instructions" and "Special Delivery
Instructions" are both completed, please issue the Quest Diagnostics Shares
and/or a check for any cash consideration or cash received in lieu of fractional
Quest Diagnostics Shares (and any accompanying documents, as appropriate) and
return any certificates for Shares not tendered or not accepted for exchange in
the Offer to the person(s) so indicated. Unless otherwise indicated below in the
box entitled "Special Payment Instructions", please credit any Shares tendered
hereby and delivered by book-entry transfer that are not accepted for payment by
crediting the account at the Book-Entry Transfer Facility designated above. The
undersigned recognizes that Purchaser has no obligation, pursuant to the Special
Payment Instructions, to transfer any Shares from the name of the registered
holder(s) thereof if Purchaser does not accept for payment any Shares tendered
hereby.

                                        5
<PAGE>

          ------------------------------------------------------------

                          SPECIAL PAYMENT INSTRUCTIONS
                        (SEE INSTRUCTIONS 1, 5, 6 AND 7)

        To be completed ONLY if the Quest Diagnostics Shares and/or the check
   for cash payable in the Offer are to be issued in the name of someone
   other than the undersigned or if the certificates for Shares not tendered
   or not accepted for exchange in the Offer are to be issued in the name of
   someone other than the undersigned.

   Issue [ ] Check and
         [ ] Certificate(s) to:

   Name:
   ----------------------------------------------------
                                    (PLEASE PRINT)

   Address:
   --------------------------------------------------

          ------------------------------------------------------------

          ------------------------------------------------------------
                                   (ZIP CODE)

          ------------------------------------------------------------
                 (TAX IDENTIFICATION OR SOCIAL SECURITY NUMBER)
                           (SEE SUBSTITUTE FORM W-9)

   Account
   Number:
   -------------------------------------------------
          ------------------------------------------------------------
          ------------------------------------------------------------

                         SPECIAL DELIVERY INSTRUCTIONS
                        (SEE INSTRUCTIONS 1, 5, 6 AND 7)

        To be completed ONLY if the Quest Diagnostics Shares and/or the check
   for cash payable in the Offer are to be sent to someone other than the
   undersigned or to the undersigned at an address other than that shown
   under "Description of Shares Tendered" or if the certificates for Shares
   not tendered or not accepted for exchange in the Offer are to be sent to
   someone other than the undersigned or to the undersigned at an address
   other than that shown under "Description of Shares Tendered".

   Mail: [ ] Check and
         [ ] Certificate(s) to:

   Name:
   ----------------------------------------------------
                                    (PLEASE PRINT)

   Address:
   --------------------------------------------------

          ------------------------------------------------------------

          ------------------------------------------------------------
                                   (ZIP CODE)

          ------------------------------------------------------------
                 (TAX IDENTIFICATION OR SOCIAL SECURITY NUMBER)
                           (SEE SUBSTITUTE FORM W-9)
          ------------------------------------------------------------

                                        6
<PAGE>

                                   IMPORTANT
                            STOCKHOLDERS: SIGN HERE
                  (Please Complete Substitute Form W-9 Below)

--------------------------------------------------------------------------------

--------------------------------------------------------------------------------
                           Signature(s) of Holder(s)

Dated:
--------------------------- , 2002.

Name(s):
--------------------------------------------------------------------------------
                                  PLEASE PRINT

Capacity (full title):
                ----------------------------------------------------------------
                               SEE INSTRUCTION 5

Address:
       -------------------------------------------------------------------------

--------------------------------------------------------------------------------
                                INCLUDE ZIP CODE

Daytime Area Code and Telephone No.:
                              --------------------------------------------------

Taxpayer Identification or Social Security No.:
                                   ---------------------------------------------

(Must be signed by registered holder(s) exactly as name(s) appear(s) on Share
Certificates or on a security position listing or by person(s) authorized to
become registered holder(s) by certificates and documents transmitted herewith.
If signature is by a trustee, executor, administrator, guardian,
attorney-in-fact, officer of a corporation or other person acting in a fiduciary
or representative capacity, please set forth full title and see Instruction 5.)

                           GUARANTEE OF SIGNATURE(S)
                   (IF REQUIRED -- SEE INSTRUCTIONS 1 AND 5)

                     FOR USE BY ELIGIBLE INSTITUTIONS ONLY.
                        PLACE GUARANTEE IN SPACE BELOW.

Name of Firm:
           ---------------------------------------------------------------------
                                  PLEASE PRINT

Address:
       -------------------------------------------------------------------------
                                INCLUDE ZIP CODE

Authorized Signature:
                ----------------------------------------------------------------

Name(s):------------------------------------------------------------------------

Area Code and Telephone Number:
                           -----------------------------------------------------

Dated:
--------------------------- , 2002

                                        7
<PAGE>

                                  INSTRUCTIONS

             Forming Part of the Terms and Conditions of the Offer

     1.  Guarantee of Signatures.  All signatures on this Letter of Election and
Transmittal must be guaranteed by a firm which is a member of the Security
Transfer Agents Medallion Signature Program, or by any other "eligible guarantor
institution", as such term is defined in Rule 17Ad-15 promulgated under the
Securities Exchange Act of 1934, as amended (each of the foregoing being, an
"Eligible Institution"), unless (i) this Letter of Election and Transmittal is
signed by the registered holder(s) of Shares (which term, for purposes of this
document, shall include any participant in the Book-Entry Transfer Facility
whose name appears on a security position listing as the owner of Shares)
tendered hereby, and such holder(s) has (have) not completed the box entitled
"Special Payment Instructions" or "Special Delivery Instructions" or (ii) such
Shares are tendered for the account of an Eligible Institution. See Instruction
5.

     2.  Delivery of Letter of Election and Transmittal and Shares; Guaranteed
Delivery Procedures.  This Letter of Election and Transmittal is to be used and
completed by stockholders of the Company if either (a) Share certificates
("Share Certificates") are to be forwarded to the Offer Exchange Agent herewith
or, (b) unless an Agent's Message (as defined below) is utilized, if delivery of
Shares is to be made pursuant to the procedure for tenders by book-entry
transfer set forth in the section entitled "The Offer -- Procedure for Tendering
and Electing" of the Prospectus.

     For a stockholder to validly tender Shares pursuant to the Offer, the
stockholder must either (a) deliver to the Offer Exchange Agent a properly
completed and duly executed Letter of Election and Transmittal (or a manually
signed facsimile thereof), together with any required signature guarantees and
any other required documents, and the certificates representing the Shares
tendered, or (b) deliver to the Offer Exchange Agent either (1) a properly
completed and duly executed Letter of Election and Transmittal (or a manually
signed facsimile thereof), together with any required signature guarantees or
(2) an Agent's Message (as defined below), in each case with any other required
documents, and must transfer the Shares tendered pursuant to the procedures for
book-entry transfer set forth herein and in the section of the Prospectus
entitled "The Offer -- Procedure for Tendering and Electing". A tender by
book-entry transfer will be complete upon receipt by the Offer Exchange Agent of
a book-entry confirmation from the Book-Entry Transfer Facility.

     In each case, the Offer Exchange Agent must receive this Letter of Election
and Transmittal and the Shares (or, in the case of a book-entry transfer, this
Letter of Election and Transmittal or the Agent's Message, and a book-entry
confirmation, as described below) at one of its addresses set forth herein prior
to the expiration of the Offer.

     Stockholders whose Share Certificates are not immediately available, who
cannot deliver their Share Certificates and all other required documents to the
Offer Exchange Agent prior to the expiration date or who cannot comply with the
book-entry transfer procedures on a timely basis may tender their Shares by
properly completing and duly executing the Notice of Guaranteed Delivery
pursuant to the guaranteed delivery procedure set forth herein and described in
"The Offer -- Procedure for Tendering and Electing -- Guaranteed Delivery" in
the Prospectus.

     Pursuant to such guaranteed delivery procedures, (i) such tender must be
made by or through an Eligible Institution, (ii) a properly completed and duly
executed Notice of Guaranteed Delivery, substantially in the form made available
by Purchaser, must be received by the Offer Exchange Agent prior to the
expiration date, and (iii) the certificates for all tendered Shares, in proper
form for transfer (or a book-entry confirmation with respect to all tendered
Shares), together with a properly completed and duly executed Letter of Election
and Transmittal (or a manually signed facsimile thereof), with any required
signature guarantees, or, in the case of a book-entry transfer, an Agent's
Message, and any other required documents must be received by the Offer Exchange
Agent within three (3) New York Stock Exchange trading days after the date of
execution of such Notice of Guaranteed Delivery.

     The term "Agent's Message" means a message, transmitted by the Book-Entry
Transfer Facility to, and received by, the Offer Exchange Agent and forming a
part of the book-entry confirmation, which states that the Book-Entry Transfer
Facility has received an express acknowledgment from the participant in the
Book-Entry Transfer Facility tendering the Shares which are the subject of the
book-entry confirmation, that the participant has received and agrees to be
bound by the terms of this Letter of Election and Transmittal and that Purchaser
may enforce the agreement against the participant.

                                        8
<PAGE>

     The signatures on this Letter of Election and Transmittal cover the Shares
tendered hereby. If Shares are forwarded to the Offer Exchange Agent in multiple
deliveries, a properly completed and duly executed Letter of Election and
Transmittal must accompany each delivery.

     THE METHOD OF DELIVERY OF THE SHARES, THIS LETTER OF ELECTION AND
TRANSMITTAL, SHARE CERTIFICATES AND ALL OTHER REQUIRED DOCUMENTS, INCLUDING
DELIVERY THROUGH THE BOOK-ENTRY TRANSFER FACILITY, IS AT THE OPTION AND RISK OF
THE TENDERING STOCKHOLDER, AND THE DELIVERY WILL BE DEEMED MADE ONLY WHEN
ACTUALLY RECEIVED BY THE OFFER EXCHANGE AGENT (INCLUDING, IN THE CASE OF
BOOK-ENTRY TRANSFER, BY BOOK-ENTRY CONFIRMATION). IF DELIVERY IS BY MAIL,
REGISTERED MAIL WITH RETURN RECEIPT REQUESTED, PROPERLY INSURED, IS RECOMMENDED.
IN ALL CASES, SUFFICIENT TIME SHOULD BE ALLOWED TO ENSURE TIMELY DELIVERY.

     No alternative, conditional or contingent tenders will be accepted and no
fractional Shares will be exchanged. By execution of this Letter of Election and
Transmittal (or a manually signed facsimile hereof), all tendering stockholders
waive any right to receive any notice of the acceptance of their Shares for
payment.

     3.  Inadequate Space.  If the space provided on the reverse hereof under
"Description of Shares Tendered" is inadequate, Share Certificate numbers, the
number of Shares evidenced by such Share Certificates and the number of Shares
tendered and any other required information should be listed on a separate
signed schedule attached hereto.

     4.  Partial Tenders (not applicable to stockholders who tender by
book-entry transfer).  If fewer than all Shares evidenced by any Share
Certificate are to be tendered to the Offer Exchange Agent hereby, fill in the
number of Shares that are to be tendered in the box entitled "Number of Shares
Tendered". In such cases, new Share Certificate(s) evidencing the remainder of
the Shares that were evidenced by the old Share Certificates will be sent to the
person(s) signing this Letter of Election and Transmittal, unless otherwise
provided in the box entitled "Special Delivery Instructions" or "Special Payment
Instructions" on the reverse hereof, as soon as practicable after the expiration
date or the termination of the Offer. All Shares represented by Share
Certificates delivered to the Offer Exchange Agent will be deemed to have been
tendered unless otherwise indicated.

     5.  Signatures on Letter of Election and Transmittal; Stock Powers and
Endorsements.  If this Letter of Election and Transmittal is signed by the
registered holder(s) of the Shares tendered hereby, the signature(s) must
correspond with the name(s) as written on the face of the Share Certificates
evidencing such Shares without alteration, enlargement or any other change
whatsoever.

     If any of the Shares tendered hereby are held of record by two or more
joint owners, all such persons must sign this Letter of Election and
Transmittal.

     If any of the Shares tendered hereby are registered in different names on
several certificates, it will be necessary to complete, sign and submit as many
separate Letters of Election and Transmittal as there are different
registrations of such certificates.

     If this Letter of Election and Transmittal is signed by the registered
holder(s) of Shares tendered hereby, no endorsements of Share Certificates or
separate stock powers are required, unless payment is to be made to, or Share
Certificates evidencing Shares not tendered or not accepted for payment are to
be issued in the name of, a person other than the registered holder(s).
Signatures on any such Share Certificates or stock powers must be guaranteed by
an Eligible Institution.

     If this Letter of Election and Transmittal is signed by a person other than
the registered holder(s) of Shares tendered hereby, the Share Certificate(s)
evidencing Shares tendered hereby must be endorsed or accompanied by appropriate
stock powers, in either case signed exactly as the name(s) of the registered
holder(s) appear(s) on such Share Certificate(s). Signatures on such Share
Certificate(s) and stock powers must be guaranteed by an Eligible Institution.

     If this Letter of Election and Transmittal or any Share Certificate or
stock power is signed by a trustee, executor, administrator, guardian,
attorney-in-fact, officer of a corporation or other person acting in a fiduciary
or representative capacity, such person should so indicate when signing, and
proper evidence satisfactory to Purchaser of the authority of such person so to
act must be submitted.

     6.  Stock Transfer Taxes.  Except as otherwise provided in this Instruction
6, the Company will pay or cause to be paid all stock transfer taxes with
respect to the sale and transfer of any Shares to it or to its order pursuant to
the Offer. If,

                                        9
<PAGE>

however, delivery of the consideration in respect of the Offer is to be made to,
or Share Certificate(s) evidencing Shares not tendered or not accepted for
payment are to be issued in the name of, any person other than the registered
holder(s), or if tendered Share Certificates are registered in the name of any
person other than the person(s) signing this Letter of Election and Transmittal,
the amount of any stock transfer taxes (whether imposed on the registered
holder(s) or such other person, or otherwise) payable on account of the transfer
to such other person will be deducted from the overall consideration paid for
such Shares exchanged, unless evidence satisfactory to the Company of the
payment of such taxes, or exemption therefrom, is submitted.

     7.  Special Payment and Delivery Instructions.  If Quest Diagnostics Shares
and/or a check for cash payable in the offer, and/or Share Certificates not
tendered or not accepted for payment, are to be issued to a person other than
the person(s) signing this Letter of Election and Transmittal, or if such check
or any such Quest Diagnostics Shares or Share Certificates are to be sent to a
person other than the signer of this Letter of Election and Transmittal or to
the person(s) signing this Letter of Election and Transmittal but at an address
other than that shown in the box entitled "Description of Shares Tendered" on
the reverse hereof, the appropriate boxes herein must be completed.

     8.  Questions and Requests for Assistance or Additional Copies.  Questions
and requests for assistance may be directed to the Information Agent or the
Dealer Manager at their respective addresses or telephone numbers set forth
below, or to your broker, dealer, commercial bank, trust company or other
nominee. Additional copies of the Prospectus, this Letter of Election and
Transmittal, the Notice of Guaranteed Delivery and the Guidelines for
Certification of Taxpayer Identification Number on Substitute Form W-9 may be
obtained from the Information Agent at the address or phone number set forth
below.

     9.  Substitute Form W-9.  Each tendering stockholder is required to provide
the Offer Exchange Agent with a correct Taxpayer Identification Number ("TIN")
on the Substitute Form W-9 which is provided under "Important Tax Information"
below, and to certify, under penalty of perjury, that such number is correct,
that such stockholder is not subject to backup withholding of federal income tax
and that such stockholder is a U.S. person. If a tendering stockholder has been
notified by the Internal Revenue Service that such stockholder is subject to
backup withholding, such stockholder must cross out item (2) of the
Certification box of the Substitute Form W-9, unless such stockholder has since
been notified by the Internal Revenue Service that such stockholder is no longer
subject to backup withholding. Failure to provide the information on the
Substitute Form W-9 may subject the tendering stockholder to a $50 penalty
imposed by the Internal Revenue Service and to federal income tax withholding at
a 30% withholding rate for any payments made to the stockholder prior to January
1, 2004. If the tendering stockholder has not been issued a TIN and has applied
for one or intends to apply for one in the near future, such stockholder should
write "Applied For" in the space provided for the TIN in Part I of the
Substitute Form W-9, and sign and date the Substitute Form W-9. If "Applied For"
is written in Part I, and the Offer Exchange Agent is not provided with a TIN
within 60 days of its receipt of the Substitute Form W-9, the Offer Exchange
Agent will withhold 30% on all payments of the purchase price made prior to
January 1, 2004 to such stockholder until a TIN is provided to the Offer
Exchange Agent.

     10.  Waiver of Conditions.  Purchaser reserves the absolute right in its
sole discretion (subject to the terms of the Merger Agreement, dated as of April
2, 2002, and amended as of May 13, 2002, among Quest Diagnostics, Purchaser and
the Company) to waive any of the specified conditions to the Offer.

     11.  Lost, Destroyed or Stolen Share Certificates.  If any Share
Certificate(s) has (have) been lost, destroyed or stolen, the stockholder should
promptly notify the Company's transfer agent, First Union National Bank
Corporate Trust, by calling 800-829-8432. The stockholder will then be
instructed as to the steps that must be taken in order to replace the Share
Certificate(s). This Letter of Election and Transmittal and related documents
cannot be processed until the procedures for replacing lost, destroyed or stolen
Share Certificates have been followed and a new Share Certificate is issued. The
replacement of a lost certificate will cost 2% of the market value of the lost
Shares or a minimum administrative surety bond filing fee of $25.00. If you have
lost your certificates, please remember to check the box on the first page of
this Letter of Election and Transmittal.

     12.  Revocation or Change of Election.  An election is irrevocable, except
that Shares tendered pursuant to the Offer may be withdrawn at any time prior to
the expiration date. After an effective withdrawal, you may change your election
by submitting to the Offer Exchange Agent a completed replacement of this
document (and any other documents required by the Offer for properly tendering
Shares) prior to the expiration of the Offer.

                                        10
<PAGE>

     13.  Election Procedure.  To properly complete the "Election" box, you must
indicate the number of Shares owned by you, the number of Shares being tendered
hereby and whether, with respect to such Shares, you are electing to receive
cash or Quest Diagnostics Shares. IF YOU FAIL TO PROPERLY MAKE AN ELECTION, YOU
WILL BE DEEMED TO HAVE ELECTED TO RECEIVE QUEST DIAGNOSTICS SHARES IN EXCHANGE
FOR ALL OF YOUR VALIDLY TENDERED SHARES, AND YOU WILL RECEIVE 0.3256 OF A QUEST
DIAGNOSTICS SHARE FOR EACH SHARE YOU VALIDLY TENDER FOR EXCHANGE.

     IMPORTANT:  THIS LETTER OF ELECTION AND TRANSMITTAL (OR MANUALLY SIGNED
FACSIMILE HEREOF), PROPERLY COMPLETED AND DULY EXECUTED, TOGETHER WITH ANY
REQUIRED SIGNATURE GUARANTEES OR, IN THE CASE OF A BOOK-ENTRY TRANSFER, AN
AGENT'S MESSAGE, AND ANY OTHER REQUIRED DOCUMENTS MUST BE RECEIVED BY THE OFFER
EXCHANGE AGENT PRIOR TO THE EXPIRATION DATE, AND EITHER CERTIFICATES FOR
TENDERED SHARES MUST BE RECEIVED BY THE OFFER EXCHANGE AGENT OR SHARES MUST BE
DELIVERED PURSUANT TO THE PROCEDURES FOR BOOK-ENTRY TRANSFER, IN EACH CASE,
PRIOR TO THE EXPIRATION DATE, OR THE TENDERING STOCKHOLDER MUST COMPLY WITH THE
PROCEDURES FOR GUARANTEED DELIVERY.

                           IMPORTANT TAX INFORMATION

     Under U.S. federal income tax law, a stockholder whose tendered Shares are
accepted for payment is generally required to provide the Offer Exchange Agent
(as payer) with such stockholder's correct TIN on Substitute Form W-9 provided
herewith. If such stockholder is an individual, the TIN generally is such
stockholder's social security number. If the Offer Exchange Agent is not
provided with the correct TIN, the stockholder may be subject to a $50 penalty
imposed by the Internal Revenue Service and payments that are made to such
stockholder with respect to Shares purchased pursuant to the Offer may be
subject to backup withholding of 30% for payments made prior to January 1, 2004.
In addition, if a stockholder makes a false statement that results in no
imposition of backup withholding, and there was no reasonable basis for making
such statement, a $500 penalty may also be imposed by the Internal Revenue
Service.

     Certain stockholders (including, among others, corporations and certain
foreign individuals) are not subject to these backup withholding and information
reporting requirements. In order for a foreign individual to qualify as an
exempt recipient, such individual must submit a statement (Internal Revenue
Service Form W-8 BEN, or other appropriate form), signed under penalties of
perjury, attesting to such individual's exempt status. Forms of such statements
can be obtained from the Offer Exchange Agent. See the enclosed "Guidelines for
Certification of Taxpayer Identification Number on Substitute Form W-9" for
additional instructions. A stockholder should consult his, her or its tax
advisor as to such stockholder's qualification for exemption from backup
withholding and the procedure for obtaining such exemption.

     If backup withholding applies, the Offer Exchange Agent is required to
withhold 30% of any payments made to the stockholder prior to January 1, 2004.
Backup withholding is not an additional tax. Rather, the federal income tax
liability of persons subject to backup withholding will be reduced by the amount
of tax withheld. If withholding results in an overpayment of taxes, a refund may
be obtained, provided that the required information is furnished to the Internal
Revenue Service.

PURPOSE OF SUBSTITUTE FORM W-9

     To prevent backup withholding on payments that are made to a stockholder,
the stockholder is required to notify the Offer Exchange Agent of such
stockholder's correct TIN by completing the form below certifying that (a) the
TIN provided on Substitute Form W-9 is correct (or that such stockholder is
awaiting a TIN) and (b) (i) such stockholder has not been notified by the
Internal Revenue Service that he, she or it is subject to backup withholding as
a result of a failure to report all interest or dividends or (ii) the Internal
Revenue Service has notified such stockholder that such stockholder is no longer
subject to backup withholding.

                                        11
<PAGE>

WHAT NUMBER TO GIVE THE OFFER EXCHANGE AGENT

     The stockholder is required to give the Offer Exchange Agent the TIN (e.g.,
social security number or employer identification number) of the record holder
of Shares tendered hereby. If Shares are in more than one name or are not in the
name of the actual owner, consult the enclosed "Guidelines for Certification of
Taxpayer Identification Number on Substitute Form W-9" for additional guidance
on which number to report. If the tendering stockholder has not been issued a
TIN and has applied for a number or intends to apply for a number in the near
future, the stockholder should write "Applied For" in the space provided for the
TIN in Part I, and sign and date the Substitute Form W-9. If "Applied For" is
written in Part I and the Offer Exchange Agent is not provided with a TIN within
60 days, the Offer Exchange Agent will withhold 30% of all payments of the
purchase price to such stockholder made prior to January 1, 2004 until a TIN is
provided to the Offer Exchange Agent.

                                        12
<PAGE>

<Table>
<S>                             <C>                                               <C>
-------------------------------------------------------------------------------------------------------------------------
                                  PAYER'S NAME: COMPUTERSHARE TRUST COMPANY OF NEW YORK
-------------------------------------------------------------------------------------------------------------------------
                                 PART I -- Taxpayer Identification Number -- For      -------------------------------
SUBSTITUTE                       all accounts, enter your taxpayer                        Social security number
 FORM W-9                        identification number in the box at right. (For                    or
 DEPARTMENT OF THE               most individuals, this is your social security
 TREASURY                        number. If you do not have a number, see             -------------------------------
 INTERNAL REVENUE SERVICE        "Obtaining a Number" in the enclosed Guide-          Employer identification number
                                 lines.) Certify by signing and dating below.     (If awaiting TIN, write "Applied For")
 PAYER'S REQUEST FOR TAXPAYER    Note: If the account is in more than one name,
 IDENTIFICATION NUMBER (TIN)     see the chart in the enclosed Guidelines to
                                 determine which number to give the payer.
                                ----------------------------------------------------------------------------------------
                                 PART II -- For Payees Exempt from Backup Withholding, see the enclosed Guidelines and
                                 complete as instructed therein.
-------------------------------------------------------------------------------------------------------------------------
</Table>

<Table>
<S>                                  <C>
CERTIFICATION -- Under penalties of perjury, I certify that:
(1) The number shown on this form is my correct Taxpayer Identification Number (or I am waiting for a number to be issued
to me),
(2) I am not subject to backup withholding because: (a) I am exempt from backup withholding, or (b) I have not been
    notified by the Internal Revenue Service (the "IRS") that I am subject to backup withholding as a result of failure
    to report all interest or dividends, or (c) the IRS has notified me that I am no longer subject to backup
    withholding, and
(3) I am a United States person (including a United States resident alien).
CERTIFICATE INSTRUCTIONS -- You must cross out item (2) above if you have been notified by the IRS that you are currently
subject to backup withholding because of underreporting interest or dividends on your tax return. However, if after being
notified by the IRS that you were subject to backup withholding you received another notification from the IRS that you
are no longer subject to backup withholding, do not cross out item (2). (Also see instructions in the enclosed
Guidelines.)
-------------------------------------------------------------------------------------------------------------------------
 SIGNATURE:  ___________________________________________________________________  DATE: ________________________, 200_
-------------------------------------------------------------------------------------------------------------------------
</Table>

NOTE:  FAILURE TO COMPLETE AND RETURN THIS FORM MAY RESULT IN BACKUP WITHHOLDING
       OF 30% OF ANY PAYMENTS MADE TO YOU PURSUANT TO THIS OFFER. PLEASE REVIEW
       THE ENCLOSED "GUIDELINES FOR CERTIFICATION OF TAXPAYER IDENTIFICATION
       NUMBER ON SUBSTITUTE FORM W-9" FOR ADDITIONAL DETAILS.

NOTE:  YOU MUST COMPLETE THE FOLLOWING CERTIFICATE IF YOU ARE AWAITING A
       TAXPAYER IDENTIFICATION NUMBER.

<Table>
<S>                                                           <C>
---------------------------------------------------------------------------------------------
                   CERTIFICATE OF AWAITING TAXPAYER IDENTIFICATION NUMBER

 I CERTIFY UNDER PENALTIES OF PERJURY THAT A TAXPAYER IDENTIFICATION NUMBER HAS NOT BEEN
 ISSUED TO ME, AND EITHER (1) I HAVE MAILED OR DELIVERED AN APPLICATION TO RECEIVE A TAXPAYER
 IDENTIFICATION NUMBER TO THE APPROPRIATE INTERNAL REVENUE SERVICE CENTER OR SOCIAL SECURITY
 ADMINISTRATION OFFICE OR (2) I INTEND TO MAIL OR DELIVER AN APPLICATION IN THE NEAR FUTURE.
 I UNDERSTAND THAT, IF I DO NOT PROVIDE A TAXPAYER IDENTIFICATION NUMBER BY THE TIME OF
 PAYMENT, 30% OF ALL REPORTABLE CASH PAYMENTS MADE TO ME THEREAFTER AND PRIOR TO JANUARY 1,
 2004 WILL BE WITHHELD UNTIL I PROVIDE A TAXPAYER IDENTIFICATION NUMBER.
  SIGNATURE: ______________________________________________________ DATE: --------------------
---------------------------------------------------------------------------------------------
</Table>

                                        13
<PAGE>

     This Letter of Election and Transmittal and certificates for Shares and any
other required documents should be sent or delivered by each stockholder or such
stockholder's broker, dealer, commercial bank, trust company or other nominee to
the Offer Exchange Agent at one of its addresses or to the facsimile number set
forth below.
                          The Offer Exchange Agent is:
                    COMPUTERSHARE TRUST COMPANY OF NEW YORK

   By Facsimile Transmission (for Eligible Institutions only): (212) 701-7636
                      Confirm by Telephone: (212) 701-7624

<Table>
<S>                                 <C>                                 <C>
             By Mail:                         By Facsimile:               By Overnight or Hand Delivery:



Computershare Trust Company of New  Computershare Trust Company of New  Computershare Trust Company of New
               York                                York                                York
       Wall Street Station             By Facsimile: (212) 701-7636             Wall Street Plaza
          P.O. Box 1010                 Telephone: (212) 701-7624           88 Pine Street, 19th Floor
  New York, New York 10268-1010                                              New York, New York 10005
</Table>

                             ---------------------

     Questions or requests for assistance may be directed to the Information
Agent or the Dealer Manager at their respective addresses and telephone numbers
listed below. Additional copies of the Prospectus, this Letter of Election and
Transmittal, the Notice of Guaranteed Delivery and other Offer materials may be
obtained from the Information Agent. A stockholder may also contact brokers,
dealers, commercial banks, trust companies or other nominees for assistance
concerning the Offer.

                    The Information Agent for the Offer is:

                          (Georgeson Shareholder Logo)

                          17 State Street, 10th Floor
                               New York, NY 10004
                     Banks and Brokers Call: (212) 440-9800
                   All Others Call Toll Free: (866) 318-0509

                      The Dealer Manager for the Offer is:

                              Merrill Lynch & Co.

                            4 World Financial Center
                            New York, New York 10080
                         Call Toll Free: (866) 276-1462

                                        14

