Exhibit 5.1




                                                November 27, 2001


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

                         Quest Diagnostics Incorporated
                         ------------------------------

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"), by the Company of the following securities of the Company
with an aggregate offering price of up to $250,000,000 or the equivalent thereof
in one or more foreign currencies: (i) senior debt securities, including the
guarantees endorsed thereon, if any, (the "Senior Debt") and subordinated debt
securities, including the guarantees endorsed thereon, if any, (the
"Subordinated Debt", and together with the Senior Debt, the "Debt Securities");
(ii) preferred stock (the "Preferred Stock") and the guarantees, if any, thereof
by subsidiaries of the Company (the "Preferred Stock Guarantees"); and (iii)
common stock (the "Common Stock"), including common stock that may be issued
upon conversion of the Debt Securities or Preferred Stock. 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 an indenture dated as of June 27, 2001, as supplemented by the First
Supplemental Indenture dated as of June 27, 2001, and as further supplemented by
the Second Supplemental Indenture dated as of November 26, 2001 (collectively,
the "Senior Indenture"), in each case, 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 The
Bank of New York, as trustee (the "Subordinated Trustee"). The



subsidiaries of the Company, if any, which are guarantors of the Preferred Stock
are referred to herein as the "Preferred Stock Guarantors". The Senior
Subsidiary Guarantors, the Subordinated Subsidiary Guarantors and the Preferred
Stock Guarantors are referred to collectively as the "Subsidiary Guarantors".

                  In our capacity as counsel to the Company we have examined (i)
the Registration Statement, (ii) the 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 and the
Subsidiary Guarantors, 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, executed,
and delivered by the Company, and assuming due authorization, execution and
delivery by each Senior Subsidiary Guarantor, and the Senior Trustee, the Senior
Indenture constitutes 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, if applicable, each Senior
Subsidiary Guarantor, 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 and, if applicable, each Senior Subsidiary Guarantor, enforceable
against the Company and each Senior Subsidiary Guarantor, as the case may be, 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

                                       2


executed by the Company and, if applicable, each Subordinated Subsidiary
Guarantor, 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 and, if applicable, each Subordinated Subsidiary Guarantor,
enforceable against the Company and each Subordinated Subsidiary Guarantor, as
the case may be, 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 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 Preferred Stock Guarantees have been duly authorized
and, when (i) the final terms thereof have been duly established and approved
and (ii) the Preferred Stock Guarantees have been duly executed by each
Preferred Stock Guarantor and delivered to and paid for by the purchasers
thereof, the Preferred Stock Guarantees will constitute valid and legally
binding obligations of each Preferred Stock Guarantor, enforceable against each
Preferred Stock Guarantor, as the case may be, in accordance with the terms
thereof.

                  7. 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.

                  The opinions set forth in paragraphs (1) through (4) and (6)
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 the Securities" in the Prospectus.

                                                  Very truly yours,


                                                  /s/  SHEARMAN & STERLING


STG/MFM