Exhibit 5.1

                                [S&S Letterhead]




                                December 11, 1996




Corning Clinical Laboratories Inc.
(to be renamed Quest Diagnostics Incorporated)
One Malcolm Avenue
Teterboro, N.J.  07608


Ladies and Gentlemen:

         We have acted as counsel to Corning Clinical Laboratories Inc., a
Delaware corporation (to be renamed Quest Diagnostics Incorporated) (the
"Company"), Corning Clinical Laboratories of Pennsylvania Inc., Corning MRL
Inc., DPD Holdings Inc., Metwest Inc., and CLMP Inc., each a Delaware
corporation (collectively, the "Delaware Guarantors"). We have also acted as
special New York counsel to Corning Clinical Laboratories Inc. (MI), a Michigan
corporation, Corning Nichols Institute Inc., a California corporation, Damon
Clinical Laboratories Inc., a Massachusetts corporation, Corning Clinical
Laboratories Inc. (CT), a Connecticut corporation, Corning Clinical Laboratories
Inc. (MA), a Massachusetts corporation, Deyor CPF/Metpath, Inc., an Ohio
corporation, Southgate Medical Services, Inc., an Ohio corporation, Corning
Clinical Laboratories Inc. (MD), a Maryland corporation, Nichols Institute
Diagnostics, a California corporation, Nomad-Massachusetts, Inc., a
Massachusetts corporation, Quest Diagnostics Incorporated (MI), a Michigan
corporation, Quest Diagnostics Incorporated (MD), a Maryland corporation,
Diagnostic Reference Services, Inc., a Maryland corporation and Pathology
Building Partnership, a Maryland partnership (collectively, the "Non-Delaware
Guarantors" and, together with the Delaware Guarantors, the "Guarantors"), in
connection with the filing by the Company and the Guarantors with the Securities
and Exchange Commission (the "Commission") of a Registration Statement on Form
S-1 (No. 333-15867) (the "Registration Statement") and the prospectus contained
in the Registration Statement (the "Prospectus"), covering the registration
under the Securities Act of 1933, as amended (the "Act"), of $150,000,000
aggregate principal amount of the Company's Senior Subordinated Notes Due 2006
(the "Notes"). The Notes are to be guaranteed on a senior subordinated basis
(the 



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"Guarantees") by the Guarantors. The Notes are to be issued pursuant to the
terms of an indenture (the "Indenture") between the Company, the Guarantors and
The Bank of New York, as trustee (the "Trustee"). The form of the Indenture and
the form of the Underwriting Agreement (the "Underwriting Agreement") among the
Company, Corning Incorporated and the underwriters are each filed as an exhibit
to the Registration Statement.

         In connection with the foregoing, we have examined originals, or copies
certified or otherwise identified to our satisfaction, of such documents and
corporate and partnership and public records as we have deemed necessary as a
basis for the opinions hereinafter expressed. In our examination, we have
assumed the genuineness of all signatures, the authenticity of all documents
presented to us as originals, the conformity to the originals of all documents
presented to us as copies, and the authenticity of the originals of such
documents. In rendering our opinion, we have relied as to factual matters, to
the extent we deem proper, upon certificates of public officials and
certificates and representations of officers of the Company and the Guarantors.

         In rendering these opinions, we have assumed (i) that each of the
Guarantors is duly organized and validly existing in its jurisdiction of
incorporation and has all requisite corporate or partnership power, as the case
may be, and authority to execute, deliver and perform its obligations under the
Indenture and the Guarantees; (ii) that the execution, delivery and performance
of the Indenture and the Guarantees have been duly authorized by all necessary
corporate or partnership action, as the case may be, on the part of each of the
Guarantors; and (iii) that each of the Guarantors will duly execute and deliver
the Indenture and the Guarantees.
 
         Our opinions expressed below are limited to the laws of the State of
New York, the General Corporation Law of Delaware and the federal law of the
United States, and we do not express any opinion herein concerning any other
law.

         Based upon the foregoing and having regard for such legal
considerations as we deem relevant, we are of the opinion that, as of the date
hereof:

         1. When the execution, delivery and performance of the Indenture and
the Notes have been duly authorized by all necessary corporate action on the
part of the Company, when the Indenture has been duly executed and delivered by
the parties thereto and when the Notes have been duly executed and issued by the
Company in accordance with the provisions of the Indenture, duly authenticated
by the Trustee in accordance with the Indenture and issued and sold by the
Company and paid for by the underwriters pursuant to the Underwriting Agreement,
the Notes will be valid and binding obligations of the Company enforceable
against the Company in accordance with their terms, except as enforcement
thereof may be limited by bankruptcy, insolvency (including, without limitation,
all laws relating to fraudulent transfers), reorganization or other similar laws
affecting enforcement of 



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creditors' rights generally and except as enforcement thereof is subject to
general principles of equity (regardless of whether enforcement is considered in
a proceeding in equity or at law).
 
         2. When the Indenture has been duly executed and delivered by the
parties thereto and when the Notes and the Guarantees endorsed thereon have been
duly executed and issued by the Company and the Guarantors in accordance with
the provisions of the Indenture, duly authenticated by the Trustee in accordance
with the Indenture and issued and sold by the Company and the Guarantors and
paid for by the underwriters pursuant to the Underwriting Agreement, the
Guarantees issued by each Guarantor will be valid and binding obligations of
such Guarantor enforceable against such Guarantor in accordance with their
terms, except as enforcement thereof may be limited by bankruptcy, insolvency
(including, without limitation, all laws relating to fraudulent transfers),
reorganization or other similar laws affecting enforcement of creditors' rights
generally and except as enforcement thereof is subject to general principles of
equity (regardless of whether enforcement is considered in a proceeding in
equity or at law).

         This opinion is being furnished to you solely for your benefit, and is
not to be used, circulated, quoted or otherwise referred to, in whole or in
part, for any other purpose without our prior written consent. It may not be
relied upon by any other person or entity.

         We hereby consent to the use of this opinion as Exhibit 5.1 to the
Registration Statement and to the use of our name under the caption "Validity of
the Notes and Guarantees" contained in the Prospectus which is included in the
Registration Statement. In giving this consent, we do not thereby concede that
we come within the category of persons whose consent is required by the Act or
the General Rules and Regulations promulgated thereunder.
 
 
                                                        Very truly yours,

                                                        /s/ Shearman & Sterling
 
STG/JMC/TJC/AGB/DEG