Exhibit 4.5

                          FIFTH SUPPLEMENTAL INDENTURE


                  FIFTH SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"),
dated as of June 27, 2001 between QUEST DIAGNOSTICS INCORPORATED, a Delaware
corporation (the "Company"), THE BANK OF NEW YORK, a New York banking
corporation, as Trustee (the "Trustee"), and the Subsidiary Guarantors parties
hereto.

                              W I T N E S S E T H :

                  WHEREAS, in accordance with Section 902 of the Indenture
relating to the 10 3/4% Senior Subordinated Notes due 2006 of the Company (the
"Securities"), dated as of December 16, 1996 (the "Indenture"), the Trustee, the
Company, and the Holders of at least a majority in principal amount at maturity
of the Securities outstanding as of the date hereof desire to amend certain
terms of the Indenture as described below;

                  WHEREAS, the Company is undertaking to amend the Indenture as
reflected in this Supplemental Indenture providing for the elimination of
certain of the covenants and agreements contained in the Indenture, and to
purchase all of the Securities tendered to the Company pursuant to the Offer to
Purchase and Consent Solicitation Statement and accompanying Consent and Letter
of Transmittal dated as of May 24, 2001 and any amendments, modifications or
supplements thereto (the "Offer and Consent Solicitation");

                  WHEREAS, all things necessary to make this Supplemental
Indenture a valid supplement to the Indenture according to its terms and the
terms of the Indenture have been done;

                  NOW, THEREFORE, the parties hereto agree as follows:

                  SECTION 1. Certain Terms Defined in the Indenture. All
capitalized terms used herein without definition herein shall have the meanings
ascribed thereto in the Indenture.

                  SECTION 2. Amendments to the Indenture. Subject to Section 3
hereof, the Indenture is hereby amended as follows:

                  (a) The application of the provisions of Article 10 of the
Indenture are hereby waived to the extent that such provisions might otherwise
interfere with the ability of the Company to enter into agreements contemplated
by, and to consummate, the Offer and Consent Solicitation.

                  (b) Effective at the time of the Company's payment, or deposit
with The Bank of New York, as Depositary for the Offer and Consent Solicitation,
of an amount of money sufficient to pay for all Securities validly tendered and
accepted pursuant to the Offer and Consent Solicitation and to make all Consent
Payments required under the Offer and Consent Solicitation:

         (i)      Sections 1008, 1009, 1010, 1011, 1012, 1013, 1015, 1016 and
                  1018 are hereby amended by deleting all such Sections in their
                  entirety and all references thereto

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                  in their entirety (including, without limitation, references
                  to the covenants which are being deleted hereby in the Events
                  of Default contained in Section 501(4) of the Indenture);

         (ii)     Clauses (iii), (iv) and (v) of Section 801 are hereby amended
                  by deleting all such clauses in their entirety and all
                  references thereto in their entirety and all references to
                  Section 801 in the Indenture shall mean Section 801 as amended
                  hereby;

         (iii)    Section 501 is hereby amended by deleting clauses (5) and (6)
                  thereof in their entirety and all references thereto in their
                  entirety; and

         (iv)     Section 1019 is hereby amended by deleting such Section in its
                  entirety and replacing it with the following and all
                  references to Section 1019 in the Indenture shall mean Section
                  1019 as amended hereby:

                  "SECTION 1019. Unrestricted Subsidiaries. The Company may at
any time designate any Person that after the date of this Indenture becomes a
Subsidiary of the Company as an "Unrestricted Subsidiary", whereupon (and until
such Person ceases to be an Unrestricted Subsidiary) such Person and each other
Person that is then or thereafter becomes a Subsidiary of such Person will be
deemed to be an Unrestricted Subsidiary. In addition, the Company may at any
time terminate the status of any Subsidiary of the Company as an Unrestricted
Subsidiary, whereupon such Subsidiary and each other Subsidiary of the Company
(if any) of which such Subsidiary is a Subsidiary will cease to be an
Unrestricted Subsidiary.

                  Notwithstanding the foregoing, no change in the status of a
Subsidiary of the Company from a Restricted Subsidiary to an Unrestricted
Subsidiary or an Unrestricted Subsidiary to a Restricted Subsidiary (other than
the change in status of a Restricted Subsidiary holding only Non-Core Assets to
an Unrestricted Subsidiary) will be effective, unless such change would not
otherwise result (after the giving of notice or the lapse of time, or both) in
an Event of Default."

         (v)      All definitions set forth in Section 101 of the Indenture that
                  relate to defined terms used solely in sections deleted by
                  this Supplemental Indenture are deleted in their entirety
                  hereby.

                  SECTION 3. Governing Law. The laws of the State of New York
shall govern this Supplemental Indenture but without giving effect to applicable
principles of conflicts of law.

                  SECTION 4. Counterparts. This Supplemental Indenture may be
signed in any number of counterparts, each of which shall be an original, with
the same effect as if the signatures thereto and hereto were upon the same
instrument

<PAGE>

                  SECTION 5. Ratification. Except as expressly amended hereby,
each provision of the Indenture shall remain in full force and effect and, as
amended hereby, the Indenture is in all respects agreed to, ratified and
confirmed by each of the Company and the Trustee.

                  SECTION 6. Effectiveness. The provisions of this Supplemental
Indenture shall become operative only on the Acceptance Date, as defined in the
Offer and Consent Solicitation.

                  IN WITNESS WHEREOF, the parties hereto have caused this
Supplemental Indenture to be duly executed as of the date first above written.

                                       QUEST DIAGNOSTICS INCORPORATED


                                       By:  /s/
                                          --------------------------------------
                                                Title:



                                       THE BANK OF NEW YORK,
                                                as Trustee


                                       By:  /s/ Marie E. Trimboli
                                          --------------------------------------
                                                Title: Assistant Vice President



<PAGE>



                                       QUEST DIAGNOSTICS
                                       INVESTMENTS INCORPORATED


                                       By /s/ Peter C. Fulweiler
                                          --------------------------------------
                                       Title: President

                                       By
                                          --------------------------------------
                                       Title:


                                       QUEST DIAGNOSTICS
                                       FINANCE INCORPORATED


                                       By /s/ Peter C. Fulweiler
                                          --------------------------------------
                                       Title: President

                                       By
                                          --------------------------------------
                                       Title:



                                       QUEST DIAGNOSTICS INCORPORATED (CT)
                                       QUEST DIAGNOSTICS INCORPORATED (MA)
                                       QUEST DIAGNOSTICS INCORPORATED (MD)
                                       QUEST DIAGNOSTICS INCORPORATED (MI)
                                       QUEST DIAGNOSTICS LABORATORIES
                                          OF PENNSYLVANIA INC.
                                       QUEST MRL INC.
                                       QUEST DIAGNOSTICS INCORPORATED (CA)
                                       LABORATORY HOLDINGS INC.
                                       DIAGNOSTIC REFERENCE SERVICES, INC.
                                       DPD HOLDINGS INC.
                                       METWEST INC.
                                       NICHOLS INSTITUTE DIAGNOSTICS
                                       QUEST HOLDINGS INCORPORATED (DE)
                                       QUEST HOLDINGS INCORPORATED (MD)
                                       QUEST HOLDINGS INCORPORATED (MI)
                                       QUEST DIAGNOSTICS INCORPORATED (OH)


                                       By: /s/ Joseph P. Manory
                                          --------------------------------------
                                       Title: Vice President & Treasurer
<PAGE>

                                       PATHOLOGY BUILDING PARTNERSHIP

                                       By Quest Diagnostics Incorporated (MD)
                                          As General Partner

                                       By: /s/ Joseph P. Manory
                                          --------------------------------------
                                       Title: Vice President & Treasurer


                                       QUEST DIAGNOSTICS LLC (IL)

                                       By: /s/ Joseph P. Manory
                                          --------------------------------------
                                       Title: Vice President & Treasurer


                                       QUEST DIAGNOSTICS CLINICAL
                                          LABORATORIES, INC. (DE)

                                       By: /s/ Joseph P. Manory
                                          --------------------------------------
                                       Title: Vice President & Treasurer


                                       QUEST DIAGNOSTICS HOLDINGS
                                          INCORPORATED (DE)

                                       By: /s/ Joseph P. Manory
                                          --------------------------------------
                                       Title: Vice President & Treasurer