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                                                                     Exhibit 5.1







                                             May 23, 2001


The Board of Directors
Quest Diagnostics Incorporated
One Malcolm Avenue
Teterboro, New Jersey 07608

                         QUEST DIAGNOSTICS INCORPORATED
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Ladies and Gentlemen:

         We have acted as counsel for Quest Diagnostics Incorporated (the
"Company") in connection with the preparation of a registration statement on
Form S-3 (the "Registration Statement") filed with the Securities and Exchange
Commission (the "Commission") relating to the offering from time to time,
pursuant to Rule 415 of the General Rules and Regulations of the Commission
promulgated under the Securities Act of 1933, as amended (the "Securities Act"),
(A) by the Company of the following securities of the Company with an aggregate
offering price of up to $600,000,000 or the equivalent thereof in one or more
foreign currencies: (i) senior debt securities (the "Senior Debt") and
subordinated debt securities (the "Subordinated Debt", and together with the
Senior Debt, the "Debt Securities"); (ii) preferred stock (the "Preferred
Stock"); and (iii) common stock (the "Common Stock"), including common stock
that may be issued upon conversion of the Debt Securities or Preferred Stock,
and (B) by SmithKline Beecham PLC of 1,500,000 shares of the Common Stock owned
by it. The Debt Securities, the Preferred Stock and the Common Stock are
collectively referred to as the "Securities". The offering of the Securities
will be as set forth in the prospectus contained in the Registration Statement
(the "Prospectus"), as supplemented by one or more supplements to the Prospectus
(each supplement, a "Prospectus Supplement").

         The Senior Debt will be issued in one or more series pursuant to a
senior indenture (the "Senior Indenture") to be entered into among the Company,
the subsidiaries of the Company indicated on the signature pages thereto, as
guarantors (the "Senior Subsidiary Guarantors"), and The Bank of New York, as
trustee (the "Senior Trustee"). The Subordinated Debt will be issued in one or
more series pursuant to a subordinated indenture (the "Subordinated Indenture")
to be entered into among the Company, the subsidiaries of the Company indicated
on the signature pages thereto, as guarantors (the "Subordinated Subsidiary
Guarantors" and, together with the Senior Subsidiary Guarantors, the "Subsidiary
Guarantors"), and The Bank of New York, as trustee (the "Subordinated Trustee").

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         In our capacity as counsel to the Company we have examined (i) the
Registration Statement, (ii) the form of Senior Indenture filed as an exhibit to
the Registration Statement, (iii) the form of Subordinated Indenture filed as an
exhibit to the Registration Statement, and (iv) the originals, or copies
identified to our satisfaction, of such corporate records of the Company,
certificates of public officials, officers of the Company and other persons, and
such other documents, agreements and instruments as we have deemed necessary as
a basis for the opinions hereinafter expressed. In our examination, we have
assumed the legal capacity of all natural persons, the genuineness of all
signatures, the authenticity of all documents submitted to us as originals, the
conformity with the originals of all documents submitted to us as copies.

         Our opinions set forth below are limited to the laws of the State of
New York, the General Corporation Law of the State of Delaware and the federal
laws of the United States and we do not express any opinion herein concerning
any other laws.

         Based on the foregoing, we are of the opinion that:


         1. The Senior Indenture has been duly authorized by the Company and,
when duly authorized by each Senior Subsidiary Guarantor, duly executed and
delivered by the Company and each Senior Subsidiary Guarantor and duly
authorized, executed and delivered by the Senior Trustee, the Senior Indenture
will constitute a valid and legally binding obligation of the Company and each
Senior Subsidiary Guarantor, enforceable against the Company and each Senior
Subsidiary Guarantor in accordance with its terms.


         2. The Senior Debt has been duly authorized and, when (i) the final
terms thereof have been duly established and approved and (ii) the Senior Debt
has been duly executed by the Company and authenticated by the Senior Trustee in
accordance with the Senior Indenture and delivered to and paid for by the
purchasers thereof, the Senior Debt will constitute valid and legally binding
obligations of the Company enforceable against the Company in accordance with
the terms thereof and will be entitled to the benefits of the Senior Indenture.


         3. The Subordinated Indenture has been duly authorized by the Company
and, when duly authorized by each Subordinated Subsidiary Guarantor, duly
executed and delivered by the Company and each Subordinated Subsidiary Guarantor
and duly authorized, executed and delivered by the Subordinated Trustee, the
Subordinated Indenture will constitute a valid and legally binding obligation of
the Company and each Subordinated Subsidiary Guarantor, enforceable against the
Company and each Subordinated Subsidiary Guarantor in accordance with its terms.


         4. The Subordinated Debt has been duly authorized and, when (i) the
final terms thereof have been duly established and approved and (ii) the
Subordinated Debt has been duly executed by the Company and authenticated by the
Subordinated Trustee in accordance with the Subordinated Indenture and delivered
to and paid for by the purchasers thereof, the Subordinated Debt will constitute
valid and legally binding obligations of the Company enforceable against the
Company in accordance with the terms thereof and will be entitled to the
benefits of the Subordinated Indenture.

         5. When (i) all corporate action necessary for issuance of the
Preferred Stock has been taken, including the adoption of a Certificate of
Designations relating thereto, (ii) the final terms of the Preferred Stock have
been duly established and approved, and (iii) the shares of


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Preferred Stock have been duly issued and delivered to and paid for by the
purchasers thereof, the Preferred Stock will be validly issued, fully paid and
non-assessable.


         6. The Company has authority pursuant to its Certificate of
Incorporation to issue up to 300,000,000 shares of Common Stock. When (i) all
corporate action necessary for the issuance of the Common Stock has been taken
and (ii) such shares of Common Stock have been duly issued and delivered to and
paid for by the purchasers thereof, the Common Stock will be validly issued,
fully paid and non-assessable.


         7. The Common Stock held by SmithKline Beecham PLC is validly issued,
fully paid and non-assessable.

         The opinions set forth in paragraphs (1) through (4) above are subject,
as to enforcement, to (i) bankruptcy, insolvency reorganization, moratorium or
other similar laws relating to or affecting creditors' rights generally
(including, without limitation, all laws relating to fraudulent transfers), (ii)
general principles of equity (regardless of whether enforcement is considered in
a proceeding in equity or at law) and (iii) provisions of law that require that
a judgment for money damages rendered by a court in the United States be
expressed only in United States dollars.

         We hereby consent to the use of this opinion as an exhibit to the
Registration Statement and to the use of our name under the heading "Validity of
Securities" in the Prospectus.


                                               Very truly yours,






STG/SHC/KWL/MFM