Filed by: Quest Diagnostics Incorporated

                       This communication is filed pursuant to Rules 165 and 425
                       promulgated under the Securities Act of 1933, as amended.

                                       Subject Company:       Unilab Corporation
                                       Commission File No.:   0-22758


FORWARD-LOOKING STATEMENTS:
This communication contains certain forward-looking statements under the Private
Securities Litigation Reform Act of 1995. These forward-looking statements,
which may include, but are not limited to, statements concerning the financial
condition, results of operations and businesses of Quest Diagnostics and Unilab
and the benefits expected to result from the contemplated transaction, are based
on management's current expectations and estimates and involve risks and
uncertainties that could cause actual results or outcomes to differ materially
from those contemplated by the forward-looking statements.

Factors that could cause or contribute to such differences may include, but are
not limited to, the risk that the conditions relating to the required minimum
tender of Unilab shares or regulatory clearance might not be satisfied in a
timely manner or at all, risks relating to the integration of the technologies
and businesses of Quest Diagnostics and Unilab, unanticipated expenditures,
changing relationships with customers, suppliers and strategic partners,
conditions of the economy and other factors described in the most recent reports
on Form 10-Q, most recent reports on Form 10-K, and other periodic reports filed
by Quest Diagnostics and Unilab with the Securities and Exchange Commission.

ADDITIONAL INFORMATION:
On May 15, 2002, Quest Diagnostics filed a Registration Statement on Form S-4
and a Schedule TO, and Unilab filed a Solicitation/Recommendation Statement on
Schedule 14D-9, with the Securities and Exchange Commission in connection with
the transaction. A Prospectus, which is part of the Registration Statement on
Form S-4, the Solicitation/Recommendation Statement on Schedule 14D-9, and
related exchange offer materials, including a letter of election and
transmittal, have been mailed to stockholders of Unilab. In addition, Quest
Diagnostics has previously filed a Statement on Schedule 13D relating to its
agreement with Kelso Investment Associates VI, L.P. and KEP VI, LLC. Investors
and stockholders of Unilab are urged to read all of these documents carefully.
These documents contain important information about the transaction and should
be read before any decision is made with respect to the exchange offer.
Investors and stockholders are able to obtain free copies of these documents
through the website maintained by the Securities and Exchange Commission at
www.sec.gov. Free copies of these documents may also be obtained from Quest
Diagnostics by directing a request to Quest Diagnostics Incorporated at One
Malcolm Avenue, Teterboro, New Jersey, 07608, or from Unilab by directing a
request to Unilab Corporation at 18448 Oxnard Street, Tarzana, California,
91356.




In addition to the Registration Statement on Form S-4, Schedule TO, Prospectus,
Solicitation/Recommendation Statement on Schedule 14D-9 and related exchange
offer materials, both Quest Diagnostics and Unilab file annual, quarterly and
special reports, proxy statements and other information with the Securities and
Exchange Commission. You may read and copy any reports, Statements or other
information filed by Quest Diagnostics or Unilab at the SEC public reference
room at 450 Fifth Street, N.W., Washington, D.C., 20549, or at any of the
Securities and Exchange Commission's other public reference rooms in New York,
New York and Chicago, Illinois. Please call the Securities and Exchange
Commission at 800-SEC-0330 for further information on the public reference
rooms. Quest Diagnostics' and Unilab's filings with the Securities and Exchange
Commission are also available to the public from commercial document-retrieval
services and at the website maintained by the Securities and Exchange Commission
at www.sec.gov.

                                      # # #




            Quest Diagnostics Incorporated
            One Malcolm Avenue
            Teterboro, New Jersey 07608

[LOGO]                                               News From Quest Diagnostics
                                                     ---------------------------

Contacts:

Laure Park (Investors): 201-393-5030
Gary Samuels (Media): 201-393-5700

                                                           FOR IMMEDIATE RELEASE
                                                           ---------------------


                    QUEST DIAGNOSTICS LAUNCHES EXCHANGE OFFER
                        FOR SHARES OF UNILAB CORPORATION

TETERBORO, N.J., MAY 15, 2002 - Quest Diagnostics Incorporated (NYSE: DGX), the
nation's leading provider of diagnostic testing, information and services,
announced that it commenced today its previously announced cash election
exchange offer for all outstanding shares of Unilab Corporation common stock.
The exchange offer is scheduled to expire on June 17, 2002. A copy of Quest
Diagnostics' prospectus and letter of transmittal, together with Unilab's
Schedule 14D-9, will be sent to Unilab's stockholders. Quest Diagnostics'
Registration Statement on Form S-4 and a Schedule TO was filed today with the
Securities and Exchange Commission.

As previously announced, in exchange for each of their Unilab shares, Unilab
stockholders may elect to receive $26.50 in cash or 0.3256 shares of Quest
Diagnostics common stock. The transaction will be effected as follows: a cash
election exchange offer in which Unilab stockholders who tender their shares
will receive, at their election, $26.50 in cash or 0.3256 shares of Quest
Diagnostics common stock in exchange for each of their Unilab shares;



followed by a stock-for-stock merger in which each Unilab common share not
tendered in the exchange offer will be converted into 0.3256 shares of Quest
Diagnostics common stock.

The aggregate amount of cash payable to Unilab stockholders will be subject to
proration if the stockholders of Unilab elect to receive cash with respect to
more than 30% of the outstanding common stock of Unilab. Unilab has
approximately 37.4 million shares of common stock outstanding on a fully diluted
basis. If the stockholders of Unilab elect to receive cash for 30% of the
outstanding common stock, and if all options are exercised, Quest Diagnostics
would issue approximately 8.5 million shares and pay approximately $297 million
in cash to stockholders of Unilab.

Kelso Investment Associates VI, L.P. and KEP VI, LLC, Unilab's largest
stockholders and the holders of approximately 42% of its currently outstanding
common stock, have agreed to tender all of their Unilab shares into the exchange
offer.

Completion of the exchange offer is subject to the satisfaction of customary
conditions, including the tender of a majority of Unilab's common stock on a
fully diluted basis, and regulatory review.

For additional information on the cash election exchange offer, Unilab
shareholders may contact Georgeson Shareholder Communications at 212-440-9800.
In addition, Merrill Lynch is the Dealer Manager for the exchange offer and may
be contacted toll free at 866-276-1462.

About Quest Diagnostics
Quest Diagnostics Incorporated is the nation's leading provider of diagnostic
testing, information and services, providing insights that enable physicians,
hospitals, managed care organizations and other healthcare professionals to make
decisions to improve health. The company offers the broadest access to
diagnostic laboratory services through its national network of laboratories and
patient service centers. Quest Diagnostics is the leading provider of esoteric
testing, including gene-based medical testing, and empowers healthcare
organizations and clinicians with state-of-the-art connectivity solutions that
improve practice management. Additional company information can be found on the
Internet at: www.questdiagnostics.com.

FORWARD-LOOKING STATEMENTS:
This communication contains certain forward-looking statements under the Private
Securities Litigation Reform Act of 1995. These forward-looking statements,
which may include, but are not limited to, statements concerning the financial
condition, results of operations and businesses of Quest Diagnostics and Unilab
and the benefits expected to result from the contemplated transaction, are based
on management's current expectations and estimates and involve risks and
uncertainties that could cause actual results or outcomes to differ materially
from those contemplated by the forward-looking statements.

Factors that could cause or contribute to such differences may include, but are
not limited to, the risk that the conditions relating to the required minimum
tender of Unilab shares or regulatory clearance might not be satisfied in a
timely manner or at all, risks relating to the integration of the technologies
and businesses of Quest Diagnostics and Unilab, unanticipated expenditures,
changing relationships with customers, suppliers and strategic partners,
conditions of the economy and other factors described in the most recent reports
on Form 10-Q, most recent reports on Form 10-K, and other periodic reports filed
by Quest Diagnostics and Unilab with the Securities and Exchange Commission.

ADDITIONAL INFORMATION:

On May 15, 2002, Quest Diagnostics filed a Registration Statement on Form S-4
and a Schedule TO, and Unilab filed a Solicitation/Recommendation Statement on
Schedule 14D-9,



with the Securities and Exchange Commission in connection with the transaction.
A Prospectus, which is part of the Registration Statement on Form S-4, the
Solicitation/Recommendation Statement on Schedule 14D-9, and related exchange
offer materials, including a letter of election and transmittal, has been mailed
to stockholders of Unilab. In addition, Quest Diagnostics has previously filed a
Statement on Schedule 13D relating to its agreement with Kelso Investment
Associates VI, L.P. and KEP VI, LLC. Investors and stockholders of Unilab are
urged to read all of these documents carefully. These documents contain
important information about the transaction and should be read before any
decision is made with respect to the exchange offer. Investors and stockholders
are able to obtain free copies of these documents through the website maintained
by the Securities and Exchange Commission at www.sec.gov. Free copies of these
documents may also be obtained from Quest Diagnostics by directing a request to
Quest Diagnostics Incorporated at One Malcolm Avenue, Teterboro, New Jersey,
07608, or from Unilab by directing a request to Unilab Corporation at 18448
Oxnard Street, Tarzana, California, 91356.




In addition to the Registration Statement on Form S-4, Schedule TO, Prospectus,
Solicitation/Recommendation Statement on Schedule 14D-9 and related exchange
offer materials, both Quest Diagnostics and Unilab file annual, quarterly and
special reports, proxy statements and other information with the Securities and
Exchange Commission. You may read and copy any reports, Statements or other
information filed by Quest Diagnostics or Unilab at the SEC public reference
room at 450 Fifth Street, N.W., Washington, D.C., 20549, or at any of the
Securities and Exchange Commission's other public reference rooms in New York,
New York and Chicago, Illinois. Please call the Securities and Exchange
Commission at 800-SEC-0330 for further information on the public reference
rooms. Quest Diagnostics' and Unilab's filings with the Securities and Exchange
Commission are also available to the public from commercial document-retrieval
services and at the website maintained by the Securities and Exchange Commission
at www.sec.gov.

                                      # # #