Document:

Exhibit 4.1

                                                                        SPECIMEN

                                     FORM OF

                           6.75% Senior Note due 2006

                  THIS NOTE IS A GLOBAL NOTE WITHIN THE MEANING OF THE INDENTURE
HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITORY OR A
NOMINEE THEREOF. THIS NOTE MAY NOT BE EXCHANGED IN WHOLE OR IN PART FOR A NOTE
REGISTERED, AND NO TRANSFER OF THIS NOTE IN WHOLE OR IN PART MAY BE REGISTERED,
IN THE NAME OF ANY PERSON OTHER THAN SUCH DEPOSITORY OR ITS NOMINEE EXCEPT IN
THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

                  UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED
REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY TO THE ISSUER OR ITS AGENT FOR
REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT AND SUCH CERTIFICATE ISSUED IN
EXCHANGE FOR THIS CERTIFICATE IS REGISTERED IN THE NAME OF CEDE & CO., OR SUCH
OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY, ANY
TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON
IS WRONGFUL, SINCE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
HEREIN.

<PAGE>

                                                                        SPECIMEN

                         QUEST DIAGNOSTICS INCORPORATED

                           6.75% Senior Note due 2006

                   Unconditionally guaranteed as to payment of
                          principal of and interest by
                            the Subsidiary Guarantors

No.  0 (Specimen)                                                   $[_________]

CUSIP: 748 34L AD2

                  Quest Diagnostics Incorporated, a Delaware corporation (herein
called the "Company," which term includes any successor Person under the
Indenture hereinafter referred to), for value received, hereby promises to pay
to Cede & Co., or registered assigns, the principal sum of $[_________] on July
12, 2006 (the "Stated Maturity") (except to the extent redeemed or repaid prior
to the Stated Maturity) and to pay interest thereon from June 27, 2001 or from
the most recent Interest Payment Date to which interest has been paid or duly
provided for semi-annually at the rate of 6.75% per annum, on January 12 and
July 12, commencing with January 12, 2002, on the Stated Maturity and on any
Redemption Date (each such date, an "Interest Payment Date") until the principal
hereof is paid or made available for payment.

                  Payment of Interest. The interest so payable, and punctually
paid or made available for payment, on any Interest Payment Date, will, as
provided in the Indenture, be paid, in immediately available funds, to the
Person in whose name this Note (or one or more Predecessor Securities) is
registered at the close of business January 1 or July 1 (whether or not a
Business Day, as defined in the Indenture), as the case may be, next preceding
such Interest Payment Date (the "Regular Record Date"). Any such interest not
punctually paid or duly provided for ("Defaulted Interest") will forthwith cease
to be payable to the Holder on such Regular Record Date, and such Defaulted
Interest, may be paid to the Person in whose name this Note (or one or more
Predecessor Securities) is registered at the close of business on a special
record date (the "Special Record Date") for the payment of such Defaulted
Interest to be fixed by the Trustee, notice whereof shall be given to Holders of
Notes not less than ten days prior to such Special Record Date, or may be paid
at any time in any other lawful manner not inconsistent with requirements of any
securities exchange on which the Notes may be listed, and upon such notice as
may be required by such exchange, all as more fully provided in said Indenture.

                  Place of Payment. Payment of interest on this Note will be
made at the Corporate Trust Office of the Trustee or such other office or agency
of the Company as may be designated for such purpose, in such coin or currency
of the United States of America as at the time of payment is legal tender for
payment of public and private debts; provided, however, that each installment of
interest and payment of principal on this Notes may at the Company's option be
paid in immediately available funds by transfer to an account maintained by the
payee located in the United States. Payment of the principal of this Note on the
Stated Maturity will be made against presentation of this Note at the office or
agency of the Company maintained for that purpose in the Borough of Manhattan,
The City of New York, in such coin or currency of the

<PAGE>

United States of America as at the time of payment is legal tender for the
payment of public and private debts.

                  Time of Payment. In any case where any Interest Payment Date,
Redemption Date, Stated Maturity shall not be a Business Day at any Place of
Payment, then (notwithstanding any other provision of the Indenture or this
Note), payment of principal or interest, if any, need not be made at such Place
of Payment on such date, but may be made on the next succeeding Business Day at
such Place of Payment with the same force and effect as if made on the Interest
Payment Date, Redemption Date, or at Stated Maturity; provided that no interest
shall accrue on the amount so payable for the period from and after such
Interest Payment Date, Redemption Date, Repayment Date, or Stated Maturity, as
the case may be.

                  Legends. The statements set forth in the restrictive legends
above are an integral part of the terms of this Note and by acceptance hereof
each Holder of this Note agrees to be subject to and bound by the terms and
provisions set forth in such legend.

                  General. This Note is one of a duly authorized issue of
securities (herein called the "Securities") of the Company, issued and to be
issued in one or more series under an indenture, dated as of June 27, 2001, as
it may be supplemented from time to time (herein called the "Indenture"),
between the Company and The Bank of New York, Trustee (herein called the
"Trustee", which term includes any successor trustee under the Indenture with
respect to a series of which this Note is a part), to which indenture and all
indentures supplemental thereto, including the supplemental indenture dated June
27, 2001 (the "Supplemental Indenture"), reference is hereby made for a
statement of the respective rights, limitations of rights, duties and immunities
thereunder of the Company, the Trustee and the Holders of the Securities, and of
the terms upon which the Securities are, and are to be, authenticated and
delivered. This Note is one of a duly authorized series of Securities designated
as "6.75 Senior Notes due 2006" (collectively, the "Notes"), initially limited
in aggregate principal amount to $[_________].

                  Further Issuance. The Company may from time to time, without
the consent of the Holders of Notes of this series, issue additional Notes (the
"Additional Notes") of this series having the same ranking and the same interest
rate, maturity and other terms as the Notes of this series. Any Additional Notes
of this series and the Notes of this series will constitute a single series
under the Indenture and all references to the Notes of this series shall include
the Additional Notes unless the context otherwise requires.

                  Book-Entry. This Note is a Global Note representing
$275,000,000 of the Notes. This Note is a "book entry" Note and is being
registered in the name of Cede & Co. as nominee of The Depository Trust Company
(the "Depository "), a clearing agency. Subject to the terms of the Indenture,
this Note will be held by a clearing agency or its nominee, and beneficial
interest will be held by beneficial owners through the book-entry facilities of
such clearing agency or its nominee in minimum denominations of $1,000 and
integral multiples thereof. As long as this Note is registered in the name of
the Depository or its nominee, the Trustee will make payments of principal and
interest on this Note by wire transfer of immediately available funds to the
Depository or its nominee. Notwithstanding the above, the final payment on this
Note will be made after due notice by the Trustee of the pendency of such
payment and only upon presentation and surrender of this Note at its principal
corporate trust office or such other

                                       2
<PAGE>

offices or agencies appointed by the Trustee for that purpose and such other
locations provided in the Indenture.

                  Guarantees. This Note is entitled to the benefits of the
Subsidiary Guarantees by each of the Subsidiary Guarantors of the due and
punctual payment and performance of the Guarantor Obligations made in favor of
the Trustee for the benefit of the Holder of this Note. Reference is hereby made
to Article Sixteen of the Indenture for a statement of the respective rights,
limitations of rights, duties and obligations under the Guarantees of each of
the Guarantors.

                  Events of Default. If an Event of Default with respect to the
Notes shall have occurred and be continuing, the principal of the Notes of this
series may be declared due and payable in the manner and with the effect
provided in the Indenture.

                  Maturity. The Notes of this series are not subject to any
sinking fund. The Notes of this series will be redeemable at any time, at the
option of the Company, in whole or from time to time in part, upon not less than
30 nor more than 60 days' prior notice, on any date prior to their maturity at a
Redemption Price, calculated pursuant to the Indenture, together with accrued
interest thereon, if any, to the Redemption Date (subject to the rights of
holders of record on the Regular Record Date that is prior to the Redemption
Date to receive interest on the relevant Interest Payment Date). In the case of
any partial redemption, selection of the Notes of this series for redemption
will be made by the Trustee by such methods, as the Trustee in its sole
discretion shall deem fair and appropriate. If any Note is to be redeemed in
part only, the notice of redemption relating to such Note shall state the
portion of the principal amount thereof to be redeemed. A new Note in principal
amount equal to the unredeemed portion thereof will be issued in the name of the
Holder thereof upon cancellation of this Note.

                  Defeasance and Covenant Defeasance. The Indenture contains
provisions for defeasance at any time of (a) the entire indebtedness of the
Company on this Note and (b) certain restrictive covenants and the related
Defaults and Events of Default, upon compliance by the Company with certain
conditions set forth therein, which provisions apply to this Note.

                  Modification and Waivers; Obligations of the Company Absolute.
The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of the Securities of each series. Such
amendment may be effected under the Indenture at any time by the Company, the
Subsidiary Guarantors and the Trustee with the consent of the Holders of not
less than a majority in aggregate principal amount of the Outstanding Notes of
each series affected thereby. The Indenture also contains provisions permitting
the Holders of not less than a majority in aggregate principal amount of the
Securities at the time Outstanding, on behalf of the Holders of all Outstanding
Securities, to waive compliance by the Company with certain provisions of the
Indenture. Furthermore, provisions in the Indenture permit the Holders of not
less than a majority in aggregate principal amount of the Outstanding Securities
of individual series to waive on behalf of all of the Holders of Securities of
such individual series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon
the Holder of this Note and upon all future Holders of this Note and of any Note

                                       3
<PAGE>

issued upon the registration of transfer hereof or in exchange hereof or in lieu
hereof, whether or not notation of such consent or waiver is made upon this
Note.

                  No reference herein to the Indenture and no provision of this
Note or of the Indenture shall alter or impair the obligation of the Company,
which is absolute and unconditional, to pay the principal of and interest on
this Note at the time, place, and rate, and in the coin or currency, herein
prescribed.

                  Limitation on Suits. As set forth in, and subject to, the
provisions of the Indenture, no Holder of any Note of this series will have any
right to institute any proceeding with respect to the Indenture or for any
remedy thereunder, unless such Holder shall have previously given to the Trustee
written notice of a continuing Event of Default with respect to this series, the
Holders of not less than 25% in principal amount of the Outstanding Notes of
this series shall have made written request, and offered reasonable indemnity,
to the Trustee to institute such proceedings as trustee, and the Trustee shall
not have received from the Holders of a majority in principal amount of the
Outstanding Notes of this series a direction inconsistent with such request and
shall have failed to institute such proceeding within 60 days; provided,
however, that such limitations do not apply to a suit instituted by the Holder
hereof for the enforcement of payment of the principal of or interest on this
Note on or after the respective due dates expressed herein.

                  Authorized Denominations. The Notes of this series are
issuable only in registered form without coupons in denominations of $1,000 or
any integral multiple thereof.

                  Registration of Transfer or Exchange. As provided in the
Indenture and subject to certain limitations herein and therein set forth, the
transfer of this Note is registrable in the Security Register upon surrender of
this Note for registration of transfer at the office or agency of the Company in
any place where the principal of and interest on this Note are payable, duly
endorsed by, or accompanied by a written instrument of transfer in form
satisfactory to the Company and the Security Registrar duly executed by, the
Holder hereof or his attorney duly authorized in writing, and thereupon one or
more new Notes, of authorized denominations and for the same aggregate principal
amount, will be issued to the designated transferee or transferees.

                  As provided in the Indenture and subject to certain
limitations herein and therein set forth, the Notes are exchangeable for a like
aggregate principal amount of Notes of different authorized denominations, as
requested by the Holders surrendering the same.

                  This Note is a Global Security. If the Depository is at any
time unwilling, unable or ineligible to continue as depository and a successor
depository is not appointed by the Company within 90 days or an Event of Default
under the Indenture has occurred and is continuing, the Company will issue
Securities in certificated form in exchange for each Global Security. In
addition, the Company may at any time determine not to have Securities
represented by a Global Security and, in such event, will issue Securities in
certificated form in exchange in whole for the Global Security representing such
Security. In any such instance, an owner of a beneficial interest in a Global
Security will be entitled to physical delivery in certificated form of
Securities equal in principal amount to such beneficial interest and to have
such Securities registered in its name. Securities so issued in certificated
form will be issued in denominations

                                       4
<PAGE>

of $1,000 or any amount in excess thereof which is an integral multiple of
$1,000 and will be issued in registered form only, without coupons.

                  No service charge shall be made for any such registration of
transfer or exchange, but the Company may require payment of a sum sufficient to
cover any tax or other governmental charge payable in connection therewith.

                  Prior to due presentment of this Note for registration of
transfer, the Company, the Trustee and any agent of the Company or the Trustee
may treat the Holder as the owner hereof for all purposes, whether or not this
Note be overdue, and neither the Company, the Trustee nor any such agent shall
be affected by notice to the contrary.

                  Defined Terms. All terms used in this Note, which are defined
in the Indenture and are not otherwise defined herein, shall have the meanings
assigned to them in the Indenture.

                  Governing Law. This Note shall be governed by and construed in
accordance with the law of the State of New York.

                                       5
<PAGE>

                  Unless the certificate of authentication hereon has been
executed by the Trustee by manual signature, this Note shall not be entitled to
any benefit under the Indenture or be valid or obligatory for any purpose.

                  IN WITNESS WHEREOF, the Company has caused this instrument to
be duly executed.

Dated:   , 2001
                                              QUEST DIAGNOSTICS INCORPORATED

                                              By:
                                                 -------------------------------
                                              Name:
Attest:                                       Title:

------------------------
Name:
Title:

                                       6
<PAGE>

                     TRUSTEE'S CERTIFICATE OF AUTHENTICATION

                  This is one of the Notes of the series designated and referred
to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned First Supplemental Indenture.

                                              THE BANK OF NEW YORK
                                              as Trustee

                                              By
                                                --------------------------------
                                                        Authorized Signatory

Dated:              , 2001

                                       7
<PAGE>

                 GUARANTEE OF THE INITIAL SUBSIDIARY GUARANTORS

                  FOR VALUE RECEIVED, each of the Initial Subsidiary Guarantors
(as such term is defined in the Indenture, as amended by the First Supplemental
Indenture), hereby, jointly and severally, unconditionally guarantees to the
Holder of the Note upon which this Subsidiary Guarantee is endorsed (the "Note")
and to the Trustee on behalf of the Holder, the prompt payment of the principal
of (and premium, if any, on) and interest (including, in case of default,
interest on principal and, to the extent permitted by applicable law, on overdue
interest and including any additional interest required to be paid according to
the terms of the Notes) on the Note, when due (whether at Stated Maturity, upon
Redemption, upon acceleration, upon tender for repayment at the option of the
Company), according to the terms hereof and the terms of the Indenture (the
"Guarantor Obligations"). This Guarantee is a guarantee of payment and not of
collection and is a continuing guarantee and shall apply to all Guarantor
Obligations whenever arising.

                  Obligations Unconditional and Absolute. The obligations of the
Initial Subsidiary Guarantors hereunder are absolute and unconditional
irrespective of the value, genuineness, validity, regularity or enforceability
of the Indenture or this Note, to the fullest extent permitted by applicable
law, irrespective of any circumstance whatsoever which might otherwise
constitute a legal or equitable discharge or defense of a surety or guarantor.
Each of the Initial Subsidiary Guarantors agrees that this Guarantee may be
enforced by the Holder of this Note without the necessity at any time of
proceeding against the Company or any other Person (including a co-guarantor) or
to pursue any other remedy or enforce any other right. Each of the Initial
Guarantors further agrees that nothing contained herein shall prevent the Holder
of this Note from suing on this Note or the Indenture or from exercising any
other rights available under this Note and the Indenture, and the exercise of
any of the aforesaid rights and shall not constitute a discharge of any Initial
Subsidiary Guarantor's obligations hereunder and under the Indenture; it being
the purpose and the intent of each Initial Subsidiary Guarantor that its
obligations under this Note and under the Indenture shall be absolute,
independent and unconditional under any and all circumstances. Neither any
Initial Subsidiary Guarantor's obligations under this Guarantee nor any remedy
for the enforcement thereof shall be impaired, modified, changed or released in
any manner whatsoever by an impairment, modification, change, release or
limitation of the liability of the Company or by reason of the bankruptcy or
insolvency of the Company. Each Initial Subsidiary Guarantor waives any and all
notice of the creation, renewal, extension or accrual of any of the Guarantor
Obligations or acceptance of this Guarantee. The Guarantor Obligations, and any
of them, shall conclusively be deemed to have been created, contracted or
incurred, or renewed, extended, amended or waived, in reliance upon this
Guarantee.

                  Subrogation. Each of the Initial Subsidiary Guarantors shall
be subrogated to all rights of the Holder of the Note against the Company in
respect of any amounts paid by such Initial Subsidiary Guarantor on account of
the Note or the Indenture; provided, however, that such Initial Subsidiary
Guarantor shall not be entitled to enforce or to receive any payments arising
out of, or based upon, such right of subrogation until the principal of (or
premium, if any, on) and interest on all Notes of this series shall have been
indefeasibly paid in full.

                                       1
<PAGE>

                  Modifications. Each Initial Subsidiary Guarantor agrees that
(a) the time or place of payment of the Guarantor Obligations may be changed or
extended, in whole or in part, to a time certain or otherwise, and may be
renewed or accelerated, in whole or in part; (b) the Company and any other party
liable for payment under the Indenture or under the Note may be granted
indulgences generally; (c) any of the provisions of this Note or the Indenture
may be modified, amended or waived; and (d) any party (including any Subsidiary
Guarantor) liable for the payment under this Note or under the Indenture may be
granted indulgences or be released; all without notice to or further assent by
such Initial Subsidiary Guarantor, which shall remain bound thereon,
notwithstanding any such exchange, compromise, surrender, extension, renewal,
acceleration, modification, indulgence or release.

                  Waiver of Rights. Each of the Initial Subsidiary Guarantors
hereby waives to the fullest extent permitted by law: (a) notice of acceptance
of this Guarantee by the Holder of this Note; (b) presentment and demand for
payment or performance of any of the Guarantor Obligations; (c) protest and
notice of dishonor or default with respect to the Guarantor Obligations; (d) all
other notices to which such Initial Subsidiary Guarantor might otherwise be
entitled.

                  Reinstatement. The obligations of the Initial Subsidiary
Guarantors under this Note and under Article Sixteen shall be automatically
reinstated if and to the extent that for any reason any payment by or on behalf
of any Person in respect of the Guarantor Obligations is rescinded or must
otherwise be restored by any Holder of the Notes of this series, whether as a
result of any proceedings in bankruptcy or reorganization or otherwise.

                  Remedies. Each of the Initial Subsidiary Guarantors further
agrees, to the fullest extent that it may lawfully do so, that as between each
such Initial Subsidiary Guarantor, on the one hand, and the Holder and the
Trustee, on the other hand, the maturity of the obligations guaranteed hereby
may be accelerated as provided in Article Five of the Indenture for the purposes
of this guarantee, notwithstanding any stay, injunction or other prohibition
extant under any applicable bankruptcy law preventing such acceleration in
respect of the obligations guaranteed hereby.

                  Rights of Contribution. The Initial Subsidiary Guarantors, in
connection with payments made hereunder, shall have contribution rights against
the other Subsidiary Guarantors as permitted under applicable law. Such
contribution rights shall be subordinate and subject in right of payment to the
obligations of the Subsidiary Guarantors under this Note and no Initial
Subsidiary Guarantor shall exercise such rights of contribution until all
Guarantor Obligations have been paid in full.

                  Limitation of Guaranty. Notwithstanding any provision to the
contrary contained herein or in the Indenture, to the extent the obligations of
any Initial Subsidiary Guarantor shall be adjudicated to be invalid or
unenforceable for any reason (including, without limitation, because of any
applicable state or federal law relating to fraudulent conveyances or transfers)
then the obligations of the Initial Subsidiary Guarantors hereunder shall be
limited to the maximum amount that is permissible under applicable law (whether
federal or state or otherwise and including, without limitation, the Bankruptcy
Code).

                                       2
<PAGE>

                  Release of Guarantors. Each of the Initial Subsidiary
Guarantors hereby covenants that its Subsidiary Guarantee will not be discharged
except by complete performance of its obligations contained in the Note, this
Subsidiary Guarantee and pursuant to the Indenture; provided, however, that if
(a) an Initial Subsidiary Guarantor does not guarantee any Indebtedness of the
Company the amount of which, when added together with any other outstanding
Indebtedness of the Company guaranteed by its Subsidiaries that are not
Subsidiary Guarantors, would exceed $50 million in the aggregate, excluding the
Notes of this series, and all outstanding Indebtedness of such Subsidiary
Guarantor would have been permitted to be incurred pursuant to Section 1011 of
the Indenture measured at the time of the release and discharge as described in
this paragraph, (b) the Notes of this series are defeased and discharged
pursuant to Article Fourteen of the Indenture, or (c) all or substantially all
of the assets of such Initial Subsidiary Guarantor or all of the capital stock
of such Initial Subsidiary Guarantor is sold (including by issuance, merger,
consolidation or otherwise) by the Company or any of its Subsidiaries, then in
each case of (a), (b) or (c) above, such Subsidiary Guarantor or the corporation
acquiring such assets (in the event of a sale or other disposition of all or
substantially all of the assets or capital stock of such Subsidiary Guarantor)
shall be automatically and without any further action on the part of any party
to the Indenture, and upon notice to the Trustee, be fully released and
discharged from all its liabilities and obligations under or in respect of the
Indenture and this Subsidiary Guarantee of the Note, and promptly upon the
request of the Company and at the expense of the Company, the Trustee shall
execute such documents and take such other action as is reasonably requested by
the Company to evidence the release and discharge of such Guarantor from all
such liabilities and obligations and shall, if applicable, certify to the
Company that such Initial Subsidiary Guarantor has no liabilities or obligations
resulting from a demand on such Initial Subsidiary Guarantor's Guarantee.

                  Defined Terms. All terms used in this Note, which are defined
in the Indenture and are not otherwise defined herein, shall have the meanings
assigned to them in the Indenture.

                  Governing Law. This Subsidiary Guarantee shall be governed by
and construed in accordance with the law of the State of New York.

                  Subject to the next following paragraph, each Initial
Subsidiary Guarantor hereby certifies and warrants that all acts, conditions and
things required to be done and performed and to have happened precedent to the
creation and issuance of this Subsidiary Guarantee and to constitute the same
valid obligation of each Initial Subsidiary Guarantor have been done and
performed and have happened in due compliance with all applicable laws.

                  (Remainder of page intentionally left blank.)

                                       3
<PAGE>

                  This Subsidiary Guarantee shall not be valid or become
obligatory for any purpose until the certificate of authentication on the Note
upon which this Subsidiary Guarantee is endorsed has been signed by the Trustee
under the Indenture referred to in this Note.

Dated:                , 2001
       ---------------
                                              QUEST DIAGNOSTICS HOLDINGS
                                              INCORPORATED

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              QUEST DIAGNOSTICS CLINICAL
                                              LABORATORIES, INC.

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              QUEST DIAGNOSTICS INCORPORATED
                                                (CA)

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:

                                       4
<PAGE>

                                              QUEST DIAGNOSTICS INCORPORATED
                                                (MD)

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              QUEST DIAGNOSTICS LLC

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              QUEST DIAGNOSTICS INCORPORATED
                                                (MI)

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              QUEST DIAGNOSTICS INCORPORATED
                                                (CT)

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:

                                       5
<PAGE>

                                              QUEST DIAGNOSTICS INCORPORATED
                                                (MA)

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              QUEST DIAGNOSTICS OF PENNSYLVANIA
                                                INC.

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              QUEST DIAGNOSTICS INCORPORATED
                                                (OH)

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              METWEST INC.

                                              By:______________________________
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:

                                       6
<PAGE>

                                              NICHOLS INSTITUTE DIAGNOSTICS

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              DPD HOLDINGS, INC.

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              DIAGNOSTICS REFERENCE SERVICES
                                                INC.

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:
                                              LABORATORY HOLDINGS INCORPORATED

                                              By:
                                                 -------------------------------
Attest:                                       Name:
                                              Title:

----------------------------
Name:
Title:

                                       7
<PAGE>

                                              PATHOLOGY BUILDING PARTNERSHIP

                                              By Quest Diagnostics Incorporated
                                                 (MD) As General Partner
Attest:
                                              By:
                                                 -------------------------------
                                              Name:
----------------------------                  Title:
Name:
Title:
                                              QUEST DIAGNOSTICS
                                              INVESTMENTS INCORPORATED

Attest:                                       By:
                                                 -------------------------------
                                              Name:
                                              Title:
----------------------------
Name:
Title:                                        By:
                                                 -------------------------------
                                              Name:
                                              Title:

                                              QUEST DIAGNOSTICS
                                              FINANCE INCORPORATED

Attest:                                       By:
                                                 -------------------------------
                                              Name:
                                              Title:
----------------------------
Name:
Title:                                        By:
                                                 -------------------------------
                                              Name:
                                              Title:

                                       8
<PAGE>Exhibit 4.2

                                                                        SPECIMEN

                                     FORM OF

                           7.50% Senior Note due 2011

                  THIS NOTE IS A GLOBAL NOTE WITHIN THE MEANING OF THE INDENTURE
HEREINAFTER REFERRED TO AND IS REGISTERED IN THE NAME OF A DEPOSITORY OR A
NOMINEE THEREOF. THIS NOTE MAY NOT BE EXCHANGED IN WHOLE OR IN PART FOR A NOTE
REGISTERED, AND NO TRANSFER OF THIS NOTE IN WHOLE OR IN PART MAY BE REGISTERED,
IN THE NAME OF ANY PERSON OTHER THAN SUCH DEPOSITORY OR ITS NOMINEE EXCEPT IN
THE LIMITED CIRCUMSTANCES DESCRIBED IN THE INDENTURE.

                  UNLESS THIS CERTIFICATE IS PRESENTED BY AN AUTHORIZED
REPRESENTATIVE OF THE DEPOSITORY TRUST COMPANY TO THE ISSUER OR ITS AGENT FOR
REGISTRATION OF TRANSFER, EXCHANGE OR PAYMENT AND SUCH CERTIFICATE ISSUED IN
EXCHANGE FOR THIS CERTIFICATE IS REGISTERED IN THE NAME OF CEDE & CO., OR SUCH
OTHER NAME AS REQUESTED BY AN AUTHORIZED REPRESENTATIVE OF THE DEPOSITORY, ANY
TRANSFER, PLEDGE OR OTHER USE HEREOF FOR VALUE OR OTHERWISE BY OR TO ANY PERSON
IS WRONGFUL, SINCE THE REGISTERED OWNER HEREOF, CEDE & CO., HAS AN INTEREST
HEREIN.

<PAGE>

                                                                        SPECIMEN

                         QUEST DIAGNOSTICS INCORPORATED

                           7.50% Senior Note due 2011

                   Unconditionally guaranteed as to payment of
                          principal of and interest by
                            the Subsidiary Guarantors

No.  0 (Specimen)                                                   $[_________]

CUSIP: 748 34L AE0

                  Quest Diagnostics Incorporated, a Delaware corporation (herein
called the "Company," which term includes any successor Person under the
Indenture hereinafter referred to), for value received, hereby promises to pay
to Cede & Co., or registered assigns, the principal sum of $[_________] on July
12, 2011 (the "Stated Maturity") (except to the extent redeemed or repaid prior
to the Stated Maturity) and to pay interest thereon from June 27, 2001 or from
the most recent Interest Payment Date to which interest has been paid or duly
provided for semi-annually at the rate of 7.50% per annum, on January 12 and
July 12, commencing with January 12, 2002, on the Stated Maturity and on any
Redemption Date (each such date, an "Interest Payment Date") until the principal
hereof is paid or made available for payment.

                  Payment of Interest. The interest so payable, and punctually
paid or made available for payment, on any Interest Payment Date, will, as
provided in the Indenture, be paid, in immediately available funds, to the
Person in whose name this Note (or one or more Predecessor Securities) is
registered at the close of business January 1 or July 1 (whether or not a
Business Day, as defined in the Indenture), as the case may be, next preceding
such Interest Payment Date (the "Regular Record Date"). Any such interest not
punctually paid or duly provided for ("Defaulted Interest") will forthwith cease
to be payable to the Holder on such Regular Record Date, and such Defaulted
Interest, may be paid to the Person in whose name this Note (or one or more
Predecessor Securities) is registered at the close of business on a special
record date (the "Special Record Date") for the payment of such Defaulted
Interest to be fixed by the Trustee, notice whereof shall be given to Holders of
Notes not less than ten days prior to such Special Record Date, or may be paid
at any time in any other lawful manner not inconsistent with requirements of any
securities exchange on which the Notes may be listed, and upon such notice as
may be required by such exchange, all as more fully provided in said Indenture.

                  Place of Payment. Payment of interest on this Note will be
made at the Corporate Trust Office of the Trustee or such other office or agency
of the Company as may be designated for such purpose, in such coin or currency
of the United States of America as at the time of payment is legal tender for
payment of public and private debts; provided, however, that each installment of
interest and payment of principal on this Notes may at the Company's option be
paid in immediately available funds by transfer to an account maintained by the
payee located in the United States. Payment of the principal of this Note on the
Stated Maturity will be made against presentation of this Note at the office or
agency of the Company maintained for that purpose in the Borough of Manhattan,
The City of New York, in such coin or currency of the

<PAGE>

United States of America as at the time of payment is legal tender for the
payment of public and private debts.

                  Time of Payment. In any case where any Interest Payment Date,
Redemption Date, Stated Maturity shall not be a Business Day at any Place of
Payment, then (notwithstanding any other provision of the Indenture or this
Note), payment of principal or interest, if any, need not be made at such Place
of Payment on such date, but may be made on the next succeeding Business Day at
such Place of Payment with the same force and effect as if made on the Interest
Payment Date, Redemption Date, or at Stated Maturity; provided that no interest
shall accrue on the amount so payable for the period from and after such
Interest Payment Date, Redemption Date, Repayment Date, or Stated Maturity, as
the case may be.

                  Legends. The statements set forth in the restrictive legends
above are an integral part of the terms of this Note and by acceptance hereof
each Holder of this Note agrees to be subject to and bound by the terms and
provisions set forth in such legend.

                  General. This Note is one of a duly authorized issue of
securities (herein called the "Securities") of the Company, issued and to be
issued in one or more series under an indenture, dated as of June 27, 2001, as
it may be supplemented from time to time (herein called the "Indenture"),
between the Company and The Bank of New York, Trustee (herein called the
"Trustee", which term includes any successor trustee under the Indenture with
respect to a series of which this Note is a part), to which indenture and all
indentures supplemental thereto, including the supplemental indenture dated June
27, 2001 (the "Supplemental Indenture"), reference is hereby made for a
statement of the respective rights, limitations of rights, duties and immunities
thereunder of the Company, the Trustee and the Holders of the Securities, and of
the terms upon which the Securities are, and are to be, authenticated and
delivered. This Note is one of a duly authorized series of Securities designated
as "7.50 Senior Notes due 2011" (collectively, the "Notes"), initially limited
in aggregate principal amount to $[_________].

                  Further Issuance. The Company may from time to time, without
the consent of the Holders of Notes of this series, issue additional Notes (the
"Additional Notes") of this series having the same ranking and the same interest
rate, maturity and other terms as the Notes of this series. Any Additional Notes
of this series and the Notes of this series will constitute a single series
under the Indenture and all references to the Notes of this series shall include
the Additional Notes unless the context otherwise requires.

                  Book-Entry. This Note is a Global Note representing
$275,000,000 of the Notes. This Note is a "book entry" Note and is being
registered in the name of Cede & Co. as nominee of The Depository Trust Company
(the "Depository "), a clearing agency. Subject to the terms of the Indenture,
this Note will be held by a clearing agency or its nominee, and beneficial
interest will be held by beneficial owners through the book-entry facilities of
such clearing agency or its nominee in minimum denominations of $1,000 and
integral multiples thereof. As long as this Note is registered in the name of
the Depository or its nominee, the Trustee will make payments of principal and
interest on this Note by wire transfer of immediately available funds to the
Depository or its nominee. Notwithstanding the above, the final payment on this
Note will be made after due notice by the Trustee of the pendency of such
payment and only upon presentation and surrender of this Note at its principal
corporate trust office or such other

                                       2
<PAGE>

offices or agencies appointed by the Trustee for that purpose and such other
locations provided in the Indenture.

                  Guarantees. This Note is entitled to the benefits of the
Subsidiary Guarantees by each of the Subsidiary Guarantors of the due and
punctual payment and performance of the Guarantor Obligations made in favor of
the Trustee for the benefit of the Holder of this Note. Reference is hereby made
to Article Sixteen of the Indenture for a statement of the respective rights,
limitations of rights, duties and obligations under the Guarantees of each of
the Guarantors.

                  Events of Default. If an Event of Default with respect to the
Notes shall have occurred and be continuing, the principal of the Notes of this
series may be declared due and payable in the manner and with the effect
provided in the Indenture.

                  Maturity. The Notes of this series are not subject to any
sinking fund. The Notes of this series will be redeemable at any time, at the
option of the Company, in whole or from time to time in part, upon not less than
30 nor more than 60 days' prior notice, on any date prior to their maturity at a
Redemption Price, calculated pursuant to the Indenture, together with accrued
interest thereon, if any, to the Redemption Date (subject to the rights of
holders of record on the Regular Record Date that is prior to the Redemption
Date to receive interest on the relevant Interest Payment Date). In the case of
any partial redemption, selection of the Notes of this series for redemption
will be made by the Trustee by such methods, as the Trustee in its sole
discretion shall deem fair and appropriate. If any Note is to be redeemed in
part only, the notice of redemption relating to such Note shall state the
portion of the principal amount thereof to be redeemed. A new Note in principal
amount equal to the unredeemed portion thereof will be issued in the name of the
Holder thereof upon cancellation of this Note.

                  Defeasance and Covenant Defeasance. The Indenture contains
provisions for defeasance at any time of (a) the entire indebtedness of the
Company on this Note and (b) certain restrictive covenants and the related
Defaults and Events of Default, upon compliance by the Company with certain
conditions set forth therein, which provisions apply to this Note.

                  Modification and Waivers; Obligations of the Company Absolute.
The Indenture permits, with certain exceptions as therein provided, the
amendment thereof and the modification of the rights and obligations of the
Company and the rights of the Holders of the Securities of each series. Such
amendment may be effected under the Indenture at any time by the Company, the
Subsidiary Guarantors and the Trustee with the consent of the Holders of not
less than a majority in aggregate principal amount of the Outstanding Notes of
each series affected thereby. The Indenture also contains provisions permitting
the Holders of not less than a majority in aggregate principal amount of the
Securities at the time Outstanding, on behalf of the Holders of all Outstanding
Securities, to waive compliance by the Company with certain provisions of the
Indenture. Furthermore, provisions in the Indenture permit the Holders of not
less than a majority in aggregate principal amount of the Outstanding Securities
of individual series to waive on behalf of all of the Holders of Securities of
such individual series certain past defaults under the Indenture and their
consequences. Any such consent or waiver shall be conclusive and binding upon
the Holder of this Note and upon all future Holders of this Note and of any Note

                                       3
<PAGE>

issued upon the registration of transfer hereof or in exchange hereof or in lieu
hereof, whether or not notation of such consent or waiver is made upon this
Note.

                  No reference herein to the Indenture and no provision of this
Note or of the Indenture shall alter or impair the obligation of the Company,
which is absolute and unconditional, to pay the principal of and interest on
this Note at the time, place, and rate, and in the coin or currency, herein
prescribed.

                  Limitation on Suits. As set forth in, and subject to, the
provisions of the Indenture, no Holder of any Note of this series will have any
right to institute any proceeding with respect to the Indenture or for any
remedy thereunder, unless such Holder shall have previously given to the Trustee
written notice of a continuing Event of Default with respect to this series, the
Holders of not less than 25% in principal amount of the Outstanding Notes of
this series shall have made written request, and offered reasonable indemnity,
to the Trustee to institute such proceedings as trustee, and the Trustee shall
not have received from the Holders of a majority in principal amount of the
Outstanding Notes of this series a direction inconsistent with such request and
shall have failed to institute such proceeding within 60 days; provided,
however, that such limitations do not apply to a suit instituted by the Holder
hereof for the enforcement of payment of the principal of or interest on this
Note on or after the respective due dates expressed herein.

                  Authorized Denominations. The Notes of this series are
issuable only in registered form without coupons in denominations of $1,000 or
any integral multiple thereof.

                  Registration of Transfer or Exchange. As provided in the
Indenture and subject to certain limitations herein and therein set forth, the
transfer of this Note is registrable in the Security Register upon surrender of
this Note for registration of transfer at the office or agency of the Company in
any place where the principal of and interest on this Note are payable, duly
endorsed by, or accompanied by a written instrument of transfer in form
satisfactory to the Company and the Security Registrar duly executed by, the
Holder hereof or his attorney duly authorized in writing, and thereupon one or
more new Notes, of authorized denominations and for the same aggregate principal
amount, will be issued to the designated transferee or transferees.

                  As provided in the Indenture and subject to certain
limitations herein and therein set forth, the Notes are exchangeable for a like
aggregate principal amount of Notes of different authorized denominations, as
requested by the Holders surrendering the same.

                  This Note is a Global Security. If the Depository is at any
time unwilling, unable or ineligible to continue as depository and a successor
depository is not appointed by the Company within 90 days or an Event of Default
under the Indenture has occurred and is continuing, the Company will issue
Securities in certificated form in exchange for each Global Security. In
addition, the Company may at any time determine not to have Securities
represented by a Global Security and, in such event, will issue Securities in
certificated form in exchange in whole for the Global Security representing such
Security. In any such instance, an owner of a beneficial interest in a Global
Security will be entitled to physical delivery in certificated form of
Securities equal in principal amount to such beneficial interest and to have
such Securities registered in its name. Securities so issued in certificated
form will be issued in denominations

                                       4
<PAGE>

of $1,000 or any amount in excess thereof which is an integral multiple of
$1,000 and will be issued in registered form only, without coupons.

                  No service charge shall be made for any such registration of
transfer or exchange, but the Company may require payment of a sum sufficient to
cover any tax or other governmental charge payable in connection therewith.

                  Prior to due presentment of this Note for registration of
transfer, the Company, the Trustee and any agent of the Company or the Trustee
may treat the Holder as the owner hereof for all purposes, whether or not this
Note be overdue, and neither the Company, the Trustee nor any such agent shall
be affected by notice to the contrary.

                  Defined Terms. All terms used in this Note, which are defined
in the Indenture and are not otherwise defined herein, shall have the meanings
assigned to them in the Indenture.

                  Governing Law. This Note shall be governed by and construed in
accordance with the law of the State of New York.

                                       5
<PAGE>

                  Unless the certificate of authentication hereon has been
executed by the Trustee by manual signature, this Note shall not be entitled to
any benefit under the Indenture or be valid or obligatory for any purpose.

                  IN WITNESS WHEREOF, the Company has caused this instrument to
be duly executed.

Dated:   , 2001
                                               QUEST DIAGNOSTICS INCORPORATED

                                               By:
                                                  ------------------------------
                                               Name:
Attest:                                        Title:

------------------------
Name:
Title:

                                       6
<PAGE>

                     TRUSTEE'S CERTIFICATE OF AUTHENTICATION

                  This is one of the Notes of the series designated and referred
to in the within-mentioned Indenture, as such is supplemented by the
within-mentioned First Supplemental Indenture.

                                               THE BANK OF NEW YORK
                                               as Trustee

                                               By
                                                  ------------------------------
                                               Authorized Signatory

Dated:              , 2001

                                       7
<PAGE>

                 GUARANTEE OF THE INITIAL SUBSIDIARY GUARANTORS

                  FOR VALUE RECEIVED, each of the Initial Subsidiary Guarantors
(as such term is defined in the Indenture, as amended by the First Supplemental
Indenture), hereby, jointly and severally, unconditionally guarantees to the
Holder of the Note upon which this Subsidiary Guarantee is endorsed (the "Note")
and to the Trustee on behalf of the Holder, the prompt payment of the principal
of (and premium, if any, on) and interest (including, in case of default,
interest on principal and, to the extent permitted by applicable law, on overdue
interest and including any additional interest required to be paid according to
the terms of the Notes) on the Note, when due (whether at Stated Maturity, upon
Redemption, upon acceleration, upon tender for repayment at the option of the
Company), according to the terms hereof and the terms of the Indenture (the
"Guarantor Obligations"). This Guarantee is a guarantee of payment and not of
collection and is a continuing guarantee and shall apply to all Guarantor
Obligations whenever arising.

                  Obligations Unconditional and Absolute. The obligations of the
Initial Subsidiary Guarantors hereunder are absolute and unconditional
irrespective of the value, genuineness, validity, regularity or enforceability
of the Indenture or this Note, to the fullest extent permitted by applicable
law, irrespective of any circumstance whatsoever which might otherwise
constitute a legal or equitable discharge or defense of a surety or guarantor.
Each of the Initial Subsidiary Guarantors agrees that this Guarantee may be
enforced by the Holder of this Note without the necessity at any time of
proceeding against the Company or any other Person (including a co-guarantor) or
to pursue any other remedy or enforce any other right. Each of the Initial
Guarantors further agrees that nothing contained herein shall prevent the Holder
of this Note from suing on this Note or the Indenture or from exercising any
other rights available under this Note and the Indenture, and the exercise of
any of the aforesaid rights and shall not constitute a discharge of any Initial
Subsidiary Guarantor's obligations hereunder and under the Indenture; it being
the purpose and the intent of each Initial Subsidiary Guarantor that its
obligations under this Note and under the Indenture shall be absolute,
independent and unconditional under any and all circumstances. Neither any
Initial Subsidiary Guarantor's obligations under this Guarantee nor any remedy
for the enforcement thereof shall be impaired, modified, changed or released in
any manner whatsoever by an impairment, modification, change, release or
limitation of the liability of the Company or by reason of the bankruptcy or
insolvency of the Company. Each Initial Subsidiary Guarantor waives any and all
notice of the creation, renewal, extension or accrual of any of the Guarantor
Obligations or acceptance of this Guarantee. The Guarantor Obligations, and any
of them, shall conclusively be deemed to have been created, contracted or
incurred, or renewed, extended, amended or waived, in reliance upon this
Guarantee.

                  Subrogation. Each of the Initial Subsidiary Guarantors shall
be subrogated to all rights of the Holder of the Note against the Company in
respect of any amounts paid by such Initial Subsidiary Guarantor on account of
the Note or the Indenture; provided, however, that such Initial Subsidiary
Guarantor shall not be entitled to enforce or to receive any payments arising
out of, or based upon, such right of subrogation until the principal of (or
premium, if any, on) and interest on all Notes of this series shall have been
indefeasibly paid in full.

                                       1
<PAGE>

                  Modifications. Each Initial Subsidiary Guarantor agrees that
(a) the time or place of payment of the Guarantor Obligations may be changed or
extended, in whole or in part, to a time certain or otherwise, and may be
renewed or accelerated, in whole or in part; (b) the Company and any other party
liable for payment under the Indenture or under the Note may be granted
indulgences generally; (c) any of the provisions of this Note or the Indenture
may be modified, amended or waived; and (d) any party (including any Subsidiary
Guarantor) liable for the payment under this Note or under the Indenture may be
granted indulgences or be released; all without notice to or further assent by
such Initial Subsidiary Guarantor, which shall remain bound thereon,
notwithstanding any such exchange, compromise, surrender, extension, renewal,
acceleration, modification, indulgence or release.

                  Waiver of Rights. Each of the Initial Subsidiary Guarantors
hereby waives to the fullest extent permitted by law: (a) notice of acceptance
of this Guarantee by the Holder of this Note; (b) presentment and demand for
payment or performance of any of the Guarantor Obligations; (c) protest and
notice of dishonor or default with respect to the Guarantor Obligations; (d) all
other notices to which such Initial Subsidiary Guarantor might otherwise be
entitled.

                  Reinstatement. The obligations of the Initial Subsidiary
Guarantors under this Note and under Article Sixteen shall be automatically
reinstated if and to the extent that for any reason any payment by or on behalf
of any Person in respect of the Guarantor Obligations is rescinded or must
otherwise be restored by any Holder of the Notes of this series, whether as a
result of any proceedings in bankruptcy or reorganization or otherwise.

                  Remedies. Each of the Initial Subsidiary Guarantors further
agrees, to the fullest extent that it may lawfully do so, that as between each
such Initial Subsidiary Guarantor, on the one hand, and the Holder and the
Trustee, on the other hand, the maturity of the obligations guaranteed hereby
may be accelerated as provided in Article Five of the Indenture for the purposes
of this guarantee, notwithstanding any stay, injunction or other prohibition
extant under any applicable bankruptcy law preventing such acceleration in
respect of the obligations guaranteed hereby.

                  Rights of Contribution. The Initial Subsidiary Guarantors, in
connection with payments made hereunder, shall have contribution rights against
the other Subsidiary Guarantors as permitted under applicable law. Such
contribution rights shall be subordinate and subject in right of payment to the
obligations of the Subsidiary Guarantors under this Note and no Initial
Subsidiary Guarantor shall exercise such rights of contribution until all
Guarantor Obligations have been paid in full.

                  Limitation of Guaranty. Notwithstanding any provision to the
contrary contained herein or in the Indenture, to the extent the obligations of
any Initial Subsidiary Guarantor shall be adjudicated to be invalid or
unenforceable for any reason (including, without limitation, because of any
applicable state or federal law relating to fraudulent conveyances or transfers)
then the obligations of the Initial Subsidiary Guarantors hereunder shall be
limited to the maximum amount that is permissible under applicable law (whether
federal or state or otherwise and including, without limitation, the Bankruptcy
Code).

                                       2
<PAGE>

                  Release of Guarantors. Each of the Initial Subsidiary
Guarantors hereby covenants that its Subsidiary Guarantee will not be discharged
except by complete performance of its obligations contained in the Note, this
Subsidiary Guarantee and pursuant to the Indenture; provided, however, that if
(a) an Initial Subsidiary Guarantor does not guarantee any Indebtedness of the
Company the amount of which, when added together with any other outstanding
Indebtedness of the Company guaranteed by its Subsidiaries that are not
Subsidiary Guarantors, would exceed $50 million in the aggregate, excluding the
Notes of this series, and all outstanding Indebtedness of such Subsidiary
Guarantor would have been permitted to be incurred pursuant to Section 1011 of
the Indenture measured at the time of the release and discharge as described in
this paragraph, (b) the Notes of this series are defeased and discharged
pursuant to Article Fourteen of the Indenture, or (c) all or substantially all
of the assets of such Initial Subsidiary Guarantor or all of the capital stock
of such Initial Subsidiary Guarantor is sold (including by issuance, merger,
consolidation or otherwise) by the Company or any of its Subsidiaries, then in
each case of (a), (b) or (c) above, such Subsidiary Guarantor or the corporation
acquiring such assets (in the event of a sale or other disposition of all or
substantially all of the assets or capital stock of such Subsidiary Guarantor)
shall be automatically and without any further action on the part of any party
to the Indenture, and upon notice to the Trustee, be fully released and
discharged from all its liabilities and obligations under or in respect of the
Indenture and this Subsidiary Guarantee of the Note, and promptly upon the
request of the Company and at the expense of the Company, the Trustee shall
execute such documents and take such other action as is reasonably requested by
the Company to evidence the release and discharge of such Guarantor from all
such liabilities and obligations and shall, if applicable, certify to the
Company that such Initial Subsidiary Guarantor has no liabilities or obligations
resulting from a demand on such Initial Subsidiary Guarantor's Guarantee.

                  Defined Terms. All terms used in this Note, which are defined
in the Indenture and are not otherwise defined herein, shall have the meanings
assigned to them in the Indenture.

                  Governing Law. This Subsidiary Guarantee shall be governed by
and construed in accordance with the law of the State of New York.

                  Subject to the next following paragraph, each Initial
Subsidiary Guarantor hereby certifies and warrants that all acts, conditions and
things required to be done and performed and to have happened precedent to the
creation and issuance of this Subsidiary Guarantee and to constitute the same
valid obligation of each Initial Subsidiary Guarantor have been done and
performed and have happened in due compliance with all applicable laws.

                  (Remainder of page intentionally left blank.)

                                       3
<PAGE>

                  This Subsidiary Guarantee shall not be valid or become
obligatory for any purpose until the certificate of authentication on the Note
upon which this Subsidiary Guarantee is endorsed has been signed by the Trustee
under the Indenture referred to in this Note.

Dated: _______________, 2001

                                               QUEST DIAGNOSTICS HOLDINGS
                                                 INCORPORATED

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               QUEST DIAGNOSTICS CLINICAL
                                                 LABORATORIES, INC.

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               QUEST DIAGNOSTICS INCORPORATED
                                                 (CA)

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:

                                       4
<PAGE>

                                               QUEST DIAGNOSTICS INCORPORATED
                                                 (MD)

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               QUEST DIAGNOSTICS LLC

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               QUEST DIAGNOSTICS INCORPORATED
                                                 (MI)

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               QUEST DIAGNOSTICS INCORPORATED
                                                 (CT)

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:

                                       5
<PAGE>

                                               QUEST DIAGNOSTICS INCORPORATED
                                                 (MA)

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               QUEST DIAGNOSTICS OF PENNSYLVANIA
                                                 INC.

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               QUEST DIAGNOSTICS INCORPORATED
                                                 (OH)

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               METWEST INC.

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:

                                       6
<PAGE>

                                               NICHOLS INSTITUTE DIAGNOSTICS

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               DPD HOLDINGS, INC.

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               DIAGNOSTICS REFERENCE SERVICES
                                                 INC.

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:
                                               LABORATORY HOLDINGS INCORPORATED

                                               By:
                                                  ------------------------------
Attest:                                        Name:
                                               Title:

----------------------------
Name:
Title:

                                       7
<PAGE>

                                               PATHOLOGY BUILDING PARTNERSHIP

                                               By Quest Diagnostics Incorporated
                                                 (MD) As General Partner
Attest:
                                               By:
                                                  ------------------------------
                                               Name:
----------------------------                   Title:
Name:
Title:
                                               QUEST DIAGNOSTICS
                                               INVESTMENTS INCORPORATED

Attest:                                        By:
                                                  ------------------------------
                                               Name:
                                               Title:
----------------------------
Name:
Title:                                         By:
                                                  ------------------------------
                                               Name:
                                               Title:

                                               QUEST DIAGNOSTICS
                                               FINANCE INCORPORATED

Attest:                                        By:
                                                  ------------------------------
                                               Name:
                                               Title:
----------------------------
Name:
Title:                                         By:
                                                  ------------------------------
                                               Name:
                                               Title:

                                       8

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