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.:         00-11839



FORWARD-LOOKING STATEMENTS:
This communication contains certain forward-looking statements. 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,
as amended, and a Schedule TO, as amended, and Unilab filed a
Solicitation/Recommendation Statement on Schedule 14D-9, as amended, 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, as amended, 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



CONTACTS:

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

                                                         FOR IMMEDIATE RELEASE


                    QUEST DIAGNOSTICS EXTENDS EXCHANGE OFFER
                              FOR SHARES OF UNILAB

TETERBORO, N.J., JULY 31, 2002 - Quest Diagnostics Incorporated (NYSE: DGX), the
nation's leading provider of diagnostic testing, information and services,
announced today that it has extended the expiration date for its previously
announced cash election exchange offer for all outstanding shares of Unilab
Corporation common stock. The offer was extended by 10 business days and will
now expire at 12:00 midnight, New York City time, on Tuesday, August 13, 2002.
The exchange offer period has been extended because the applicable waiting
period under the Hart-Scott-Rodino Antitrust Improvements Act of 1976, as
amended, has not yet expired or been terminated.


As of 12:00 midnight, New York City time, on July 30, 2002, approximately 31.7
million shares of Unilab Corporation common stock had been tendered,
representing more than 94% of the outstanding Unilab Corporation common stock.

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. 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,
as amended, and a Schedule TO, as amended, and Unilab filed a
Solicitation/Recommendation Statement on Schedule 14D-9, as amended, 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, as amended, 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.

                                      # # #