<PAGE>

                                                                   EXHIBIT 10.14

                   LABORATORY CORPORATION OF AMERICA HOLDINGS
                                  ("LabCorp")
                                MASTER AGREEMENT

================================================================================

This Agreement between CYTYC Corporation hereinafter referred to as CYTYC, a
Delaware Corporation whose principal place of business is located at 85 Swanson
Road, Boxborough, Massachusetts-01719, and Laboratory Corporation of America
Holdings, ("LabCorp"), at LabCorp's option "LabCorp" shall also refer to any or
all of LabCorp's subsidiaries. This Agreement, together with any Product Addenda
hereto, sets forth the Terms and Conditions upon which CYTYC will sell to
"LabCorp" and "LabCorp" will purchase various diagnostic products. In the event
of any inconsistencies between this Agreement and any Product Addenda, this
Master Agreement shall control. The parties agree as follows:

A.   In consideration of "LabCorp" purchasing from CYTYC, the diagnostic
     products, equipment and related software, hereinafter collectively referred
     to as "Product", specified in the attached Product Addenda during the term
     of this Agreement, CYTYC agrees to sell such Product to "LabCorp" at the
     purchase prices specified. This Agreement supersedes all prior contracts
     between the parties, and at LabCorp's option any prior contracts between
     CYTYC and LabCorp's subsidiaries.

B.   "LabCorp", on a reasonable efforts basis, will notify CYTYC in writing of
     all acquisitions, additional locations and location changes. Upon request
     from LabCorp, CYTYC shall make product available to acquisitions and
     additional locations at the "LabCorp" pricing set forth herein.

C.   The term of the Agreement shall commence on February 1, 2000 and remain in
     effect until January 31, 2003.

D.   CYTYC shall ship to any "LabCorp" laboratory which orders Product who is
     authorized under this Agreement. Invoices should be mailed to the following
     address:

                               SEND INVOICES TO:

                    Laboratory Corporation of America Holdings
                    The Office of Diagnostic Contracts - Martha Story
                    112 Orange Drive
                    Elon College, NC 27244

     Payment is net thirty (30) days. "LabCorp" is taxable based on shipment
     destination and all applicable local/state taxes are the responsibility of
     "LabCorp". In those states where CYTYC collects local/state sales taxes,
     CYTYC will add these taxes to the invoices and remit to the appropriate
     taxing authority.

E.   Shipment shall be made FOB Destination Freight Prepaid, no additional
     handling charges or associated fees.

F.   Neither party shall assign or transfer this Agreement without the consent
     of the other party, which consent shall not be unreasonably withheld or
     delayed.

<TABLE>
<S>                          <C>                                                     <C>
LabCorp/CYTYC Corporation    The Office of Diagnostic Contracts/ms                   Page 1 of 4
LCAMA Rev. Date 11/11/1999   Acknowledgement by parties:   LabCorp                   CYTYC /s/ Illegible 2/22/2000
                                                                   ---------------         -----------------------
</TABLE>

<PAGE>

           LABORATORY CORPORATION OF AMERICA HOLDINGS MASTER AGREEMENT

================================================================================

G.   Notices and other communications permitted or required under this Agreement
     will be deemed to be properly given if in writing and either delivered by
     hand or mailed by First Class U.S. Mail postage prepaid, addressed to the
     parties as follows:

     SELLER:        CYTYC Corporation
                    85 Swanson Road
                    Boxborough, MA 01719
                    Attention: Patrick J. Sullivan, President

     "LabCorp":     Laboratory Corporation of America Holdings
                    112 Orange Drive
                    Elon College, N.C. 27244
                    Attention: Mrs. Gail Page
                    Carbon Copy to:
                    Laboratory Corporation of America Holdings
                    430 South Spring Street
                    Burlington, N.C. 27215
                    Attention: Law Department

H.   This Agreement may not be amended or modified except by written agreement
     of both of the parties. If no agreement is reached, CYTYC may, as its sole
     and exclusive remedy, terminate this Agreement provided however CYTYC shall
     be entitled to return at no charge to "LabCorp" all inventory in possession
     of "LabCorp" and payment for Product previously shipped and processed
     billable by "LabCorp". In no event shall "LabCorp" be liable for monetary
     damages. LabCorp does not warrant or represent any specific amount of
     Product shall be ordered hereunder.

I.   CYTYC will not be liable for any failure to perform under this Agreement
     due to strikes, fire, explosion, flood, riot, lock-out, injunction,
     interruption of transportation, or unavoidable accidents.

J.   CYTYC guarantees "LabCorp" the Product supplied shall not be adulterated or
     misbranded within the meaning of the U.S. Food, Drug, and Cosmetic Act.

K.   CYTYC and "LabCorp" will conduct quarterly business reviews to discuss
     technical performance of all Product included in this Agreement. In the
     event that technical problems are identified or a CYTYC product is
     unavailable, "LabCorp" will notify CYTYC of the problem in writing. CYTYC
     will, within the course of ten (10) working days, identify an action plan
     to correct the problem and deliver this, in writing, to "LabCorp". If,
     after an additional twenty (20) working days, progress is not demonstrated
     in resolving the problem or Product performance does not meet package
     insert claims, then "LabCorp" may discontinue use of that Product without
     affecting the terms and conditions of the Agreement.

L.   This Agreement may be terminated by either party with or without cause at
     any time with ninety (90) days written notice unless there are quality or
     shipment problems. If quality or shipment problems occur, then Paragraph K
     (above) applies. Quality or shipment problems are defined as inconsistent
     shipments, inadequate Product availability, Product that do not meet
     package insert claims or performance specifications as published in the
     manufacturer's publications.

<TABLE>
<S>                        <C>                                                     <C>
LabCorp/CYTYC              Term: January 1, 2000 thru December 31, 2002            Page 2 of 4
LCAMA Rev. Date 11/11/99   Acknowledgement by parties:   LabCorp                   CYTYC /s/ Illegible 2/22/2000
                                                                 ---------------         -----------------------
</TABLE>

<PAGE>

LABORATORY CORPORATION OF AMERICA HOLDINGS MASTER AGREEMENT

M.   If an individual Product becomes standardized across all Laboratory
     Corporation of America Holdings laboratories, both parties will negotiate a
     price change for the Product and amend or add a Product Addenda. If no
     Agreement is reached, either party may terminate this Agreement upon 90
     days written notice. For CYTYC, such termination shall be its sole and
     exclusive remedy.

N.   Items defined as Product listed on Addenda or added on Addenda (added at a
     later date) will have guaranteed pricing through the term of the Agreement.

O.   If any terms of this Agreement are not met by "LabCorp" and the parties
     cannot agree on a resolution, CYTYC may elect, as its sole and exclusive
     remedy, to terminate this Agreement provided however CYTYC shall be
     entitled to return at no charge to "LabCorp" all inventory in possession of
     "LabCorp" and payment for Product previously shipped and processed
     billables by "LabCorp".

P.   CYTYC warrants that during their applicable shelf life, the disposable
     Product will conform with the Specifications set forth in the package
     insert and the instrumentation and accompanying software will operate in
     accordance with the specifications and warranties set forth on Exhibit
                                                                            ---
     attached hereto and incorporated herein by reference. Furthermore, CYTYC
     hereby represents and warrants that the use of any technology or U.S.
     patents licensed hereunder is and will be free of any infringement of U.S.
     patents of other persons. CYTYC hereby represents and warrants that the use
     and sale of any Product covered by this agreement is and will be free of
     any infringement of patents of other persons. No disclaimer of warranties
     or attempt to limit "LabCorp"'s indemnification rights by CYTYC shall be
     effective.

Q.   CYTYC shall give "LabCorp" a 120 day written notification of any Product
     changes.

R.   "LabCorp" may advertise and promote CYTYC's Product and use CYTYC's
     trademarks solely in the manner used by CYTYC and for the purpose of
     marketing the Product. Customer shall not make any representation or
     warranty with respect to the Product other than those made by CYTYC.

S.   CYTYC agrees to defend, indemnify, and hold "LabCorp" and subsidiaries,
     directors, officers, employees, and agents wholly harmless from and against
     third-party claims, losses, damages, lawsuits, settlements, demands,
     causes, judgments, expenses, and cost (including reasonable attorney fees)
     (collectively "Expenses") arising or alleged under or in connection with
     this Agreement or LabCorp's use of Product under this Agreement to the
     extent that such cost and liabilities are caused by a) CYTYC breach of any
     of its warranties in this Agreement, b) the failure of Product to function
     properly for "LabCorp"'s intended use in accordance with the specifications
     in the package insert for the Product, c) any negligence or willful
     misconduct of CYTYC, or d) any other liability resulting from "LabCorp"'s
     use of the Product in accordance with the specifications in the package
     insert for the Product. However, the foregoing rights to indemnity shall
     not apply to the extent that such claim, loss, lawsuit, or settlement
     results from "LabCorp"'s employees, or from the modification of any product
     of CYTYC by a third party not within CYTYC's control or without CYTYC's
     permission. This defense, indemnity and hold harmless obligation shall also
     include, but is not limited to, any such third-party claims, losses,
     damages, lawsuits, settlements, demands, causes, judgments, expenses and
     costs (including reasonable attorney fees) against LabCorp which relate in
     any manner to LabCorp's alleged infringement of any property rights of a
     third party in or to the Product or licenses under this Agreement. In the
     event of a lawsuit or other action in connection with which LabCorp is
     seeking indemnification from CYTYC hereunder, LabCorp agrees to give timely
     notice of the lawsuit or action to CYTYC and to cooperate with CYTYC in the
     defense of the lawsuit or action.

<TABLE>
<S>                        <C>                                                     <C>
LabCorp/CYTYC              Term: January 1, 2000 thru December 31, 2002            Page 3 of 4
LCAMA Rev. Date 11/11/99   Acknowledgement by parties:   LabCorp                   CYTYC /s/ Illegible 2/22/2000
                                                                 ---------------         -----------------------
</TABLE>

<PAGE>

LABORATORY CORPORATION OF AMERICA HOLDINGS MASTER AGREEMENT

T.   CYTYC and "LabCorp" each acknowledge that the other has a proprietary
     interest in its legal and business name and reputation. Therefore, except
     as otherwise required by law, neither party shall use the other's name nor
     shall mention or describe this Agreement or its relationship with the other
     party in any press release, advertising, marketing, and promotional
     materials or other publications or materials without first obtaining the
     prior written approval of (a) in the case of LabCorp, the Senior Vice
     President of Automation and Diagnostics, or (b) in the case of CYTYC, the
     Vice President of Finance. A violation of this paragraph shall be
     considered a material breach of this Agreement, and the non-breaching party
     shall be, to the extent consistent with applicable law, entitled to pursue
     all legal or equitable remedies, including an injunction, as a result of
     such breach. Except as otherwise required by law, each of the parties
     hereto agrees to keep the terms and conditions of this Agreement (including
     any Product Addenda) confidential and will not disclose the same without
     the prior written consent of the other party. Notwithstanding the foregoing
     sentence, either party may disclose the terms and conditions of this
     Agreement (including any Product Addenda) to any employees, agents, or
     advisors of such party with a material need to know such information,
     provided that all such employees, agents and advisors agree to be bound by
     the terms and conditions of the foregoing sentence as if they were parties
     hereto, and neither party may disclose any such terms and conditions to any
     competitor of the other party.

U.   Upon termination of this Agreement for any reason, "LabCorp" shall return
     all Product to CYTYC, at CYTYC's expense that were delivered to "LabCorp"
     by CYTYC and not paid for by "LabCorp" during the term of the Agreement.
     CYTYC shall be entitled to a return at no charge to "LabCorp" of all
     inventory in possession of "LabCorp" and payment for Product previously
     shipped and processed billable.

V.   This Agreement shall be construed and enforced in accordance with the laws
     of the State of North Carolina. In the event of any default in the payment
     of any amounts due hereunder, the prevailing party in any action shall be
     entitled to collect all costs, expenses (including reasonable attorney's
     fees) and damages incurred in enforcing this Agreement.

   In the event of any inconsistencies between this Agreement and the attached
                  Addenda, this Master Agreement shall control.

LABORATORY CORPORATION OF AMERICA               CYTYC CORPORATION
HOLDINGS


By:    /s/ Nevin Breedlove                By:    /s/ Daniel J. Levangie
       --------------------------------          -------------------------------
       Nevin Breedlove
Title: National Director of               Title: Senior Vice President
       Automation & Diagnostics
Date:                                     Date:  2/15/00
       --------------------------------          -------------------------------

<TABLE>
<S>                        <C>                                                     <C>
LabCorp/CYTYC              Term: January 1, 2000 thru December 31, 2002            Page 4 of 4
LCAMA Rev. Date 11/11/99   Acknowledgement by parties:   LabCorp                   CYTYC /s/ Illegible 2/22/2000
                                                                 ---------------         -----------------------
</TABLE>

<PAGE>

         LABORATORY CORPORATION OF AMERICA HOLDINGS /CYTYC CORPORATION
                               EQUIPMENT ADDENDUM

CYTYC Corporation hereinafter referred to as CYTYC, will sell to Laboratory
Corporation of America Holdings (LabCorp) new ThinPrep 2000 Processor
instrumentation, as ordered from time to time by LabCorp, at ***% discount from
List Price for the term of this Agreement and the following terms and conditions
shall apply:

INSTRUMENT(S) PRICING ThinPrep(R) 2000 Processor

     Discount ***% off List Price as set forth below:

     ===========================================================================
     INSTRUMENT                              LIST PRICE                LCA PRICE
     ===========================================================================
     ThinPrep(R)2000 Processor                  $***                   $*** each
     ===========================================================================

SHIPPING & HANDLING

     Includes all Installation fees and Shipping charges as set forth in the
     Master Agreement.

ThinPrep(R) 2000 SERVICE AGREEMENT

     .    CYTYC will provide ThinPrep(R) 2000 Processor Service Agreement to
          LabCorp based upon the following discounted pricing schedule. Service
          contract pricing below is quoted on a "per facility" basis,
          reorganizing service economics due to multiple instruments at a single
          facility.

          ----------------------------------------------------------------------
                                                                 Total Service
          Length of Service Agreement        Annual Price     Price per facility
          ----------------------------------------------------------------------
          1 year                                 $***               $***
          ----------------------------------------------------------------------
          3 years                                $***               $***
          ----------------------------------------------------------------------
          5 years                                $***               $***
          ----------------------------------------------------------------------

     .    Either party may terminate this Service Agreement if the other party
          materially breaches any provision hereof. In the event of such
          termination the amount paid for the service contract will be prorated
          and refunded to LabCorp.

     .    CYTYC will perform corrective maintenance (Service) on the ThinPrep(R)
          2000 Processors at no additional charge to LabCorp during the 3-year
          term of this agreement. Service will be provided by one of the
          following methods at the sole discretion of LabCorp:

               1.   Repairing the instrument in the laboratory.
               2.   Replacing out the system while repairs are being performed.
               3.   Replacing the instruments permanently.

<TABLE>
<S>                                                                                <C>
EQPPA Rev, Date 4/99 The Office of Diagnostic Contracts   LabCorp/CYTYC            Page 1 of 2
                                                                                   /s/ Illegible 2/22/2000
</TABLE>

<PAGE>

          LABORATORY CORPORATION OF AMERICA HOLDINGS/CYTYC CORPORATION
                               EQUIPMENT ADDENDUM

ThinPrep(R)2000 SERVICE AGREEMENT                          continued from Page 1

..    Additional Services shall include but are not limited to the
     following:

          Toll free 24 hour phone service, 7 days per week.
          On-site field service response within 24-48 hours
          Annual Preventive Maintenance visit
          On-site technical lectures for staff, if requested by LabCorp
          Technical Service Representative visits as requested

..    CYTYC agrees to upgrade any and all CYTYC ThinPrep Processor 2000
     instruments to maintain instruments at fully operational levels
     required by LabCorp throughout the term of this Agreement. LabCorp
     shall not incur any additional costs, expense, or liability as a
     result of these upgrades.

TRAINING:

CYTYC agrees to provide, at its expense, training for one (1) Cytopathologist
and one (1) Cytotechnologist from each LabCorp laboratory that has not
previously performed the ThinPrep Pap Test in its laboratory facility, at CYTYC
a headquarters in Boxborough, MA. For laboratories that have been trained by
CYTYC at CYTYC's headquarters in Boxborough, MA, additional training of
laboratory personnel will be conducted by CYTYC Corporation Cytology
Application Specialists. This additional training will be conducted at LabCorp
laboratories. Requests by LabCorp for additional on-site training will be
conducted at LabCorp laboratories. Requests by LabCorp for additional on-site
training can be scheduled and coordinated through CYTYC Corporation Technical
Service Department.

In the event of any inconsistencies between this Addenda and Master Agreement,
the Master Agreement shall control.

PRICING EFFECTIVE DATE: January 1, 2000      EXPIRES: January 31, 2003

LABORATORY CORPORATION OF AMERICA HOLDINGS   CYTYC CORPORATION


By:                                       By: /s/ Daniel J. Levangie
   ------------------------------------       ----------------------------------
       Nevin Breedlove
Title: National Director                  Title: Senior Vice President
       Automation & Diagnostics
Date:                                     Date:  2/15/00
       --------------------------------

<TABLE>
<S>                                                                                <C>
EQPPA Rev, Date 4/99   The Office of Diagnostic Contracts   LabCorp/CYTYC          Page 2 of 2
                                                                                   /s/ Illegible 2/22/2000
</TABLE>

<PAGE>

          LABORATORY CORPORATION OF AMERICA HOLDINGS/CYTYC CORPORATION
                                PRODUCT ADDENDUM

This addendum is an integral part of the Master Agreement dated February 1, 2000
between Laboratory Corporation of America Holdings ("LabCorp") and Cytyc
Corporation ("CYTYC"). CYTYC agrees to provide to "LabCorp" the ThinPrep(R) Pap
Test(TM) ("TPPT") on the following terms and conditions:

PRICING LAB SUPPLIES:

CYTYC agrees to provide LabCorp with ThinPrep Pap Test kits as configured in
CYTYC's standard product packaging on a consignment basis. These supplies will
be billed to "LabCorp" following the fifth business day of each month at a
Product pricing of $*** per billable. On or before the fifth business day of
each month, "LabCorp" will report to CYTYC the number of ThinPrep Pap Tests
processed during the previous month.

CONSIGNMENT TERMS:

Upon not less than 90 days' notice by CYTYC to LabCorp, LabCorp shall promptly
return to CYTYC any Products provided to LabCorp hereunder, provided, however,
LabCorp shall immediately return any Product in its possession upon notice by
CYTYC of a material breach by LabCorp of any provision of this Agreement.
Notwithstanding, LabCorp shall not be obligated at any time to return to CYTYC
any physician office supplies previously provided to physicians by LabCorp under
this Agreement. LabCorp shall use reasonable efforts to return all Product, in
its possession within such 90 day period. All associated costs of return of such
Product shall be at CYTYC's sole expense. CYTYC shall bear all risk of loss for
such consigned Product whether at LabCorp location or physician third party
location. During the term of this Agreement and any return to CYTYC, CYTYC shall
insure all such Product.

       In the event of any inconsistencies between this Addenda and Master
                 Agreement, the Master Agreement shall control.

PRICING EFFECTIVE DATE: February 1, 2000            EXPIRES: January 31, 2003

LABORATORY CORPORATION OF AMERICA                        CYTYC CORPORATION
            HOLDINGS


By: /s/ Nevin Breedlove                   By: /s/ Daniel J. Levangie
    -----------------------------------       ----------------------------------
       Nevin Breedlove
Title: National Director                  Title: Senior Vice President
       Automation & Diagnostics
Date:  2/21/00                            Date:  2/15/00

<TABLE>
<S>                                                                                <C>
Acknowledged by:    LabCorp             CYTYC                                      Page 1 of 1
                            -----------       ----------                           /s/ Illegible 2/22/00
</TABLE>

<PAGE>

                                  AMENDMENT TO

                                MASTER AGREEMENT

This Amendment is entered into this 20th day of December 2001, by and between
CYTYC Corporation ("Cytyc") and Laboratory Corporation of America Holdings
("LabCorp") and is intended by the parties hereto to modify the Master Agreement
and Equipment and Product Addenda entered into between Cytyc and LabCorp dated
the 1st day of January 2000 (the "Agreement").

Cytyc and LabCorp hereby agree as follows:

1.   TERM: The term of the Agreement shall be extended through December 31,
     2004.

2.   CYTYC shall ship to any "LabCorp" laboratory, which orders Product who is
     authorized under this Agreement. Invoices should be mailed to the following
     address:

                          SEND INVOICES TO:

               Laboratory Corporation of America Holdings
               Accounts Payable Department
               Caller # 2280
               Burlington, North Carolina 27216-2280

3.   Shipment shall be FOB Factory Freight Prepaid. Payment is net thirty (30)
     days. Where applicable, there shall be added to the Charges any taxes on
     such Charges, including but not limited to, applicable state and local
     sales, use or excise taxes. Applicable sales taxes will be based upon
     shipment destination and will be added to the Charges and invoiced to
     LabCorp by Cytyc Corporation. Cytyc shall be responsible for all income
     taxes related to the income generated from the sale of products hereunder.

4.   PRE-JANUARY 1, 2002, FEE SCHEDULE: All charges for ThinPrep 2000 Processor
     Instruments shipped to LabCorp between January 1, 2001, and December 31,
     2001, shall be included in the cost per billable fee schedule effective
     through December 31, 2001, as specifically set forth in the Product
     Addendum. Title to and risk of loss for such instrumentation shall remain
     with Cytyc.

5.   INSTRUMENTATION: Effective January 1, 2002, and continuing throughout the
     remainder of the term, Cytyc shall provide all ThinPrep 2000 Processors as
     follows:

     a.   The charges for all ThinPrep 2000 Processors placed at LabCorp
          facilities prior to January 1, 2002, shall be included in the rates
          LabCorp shall pay Cytyc as more specifically set forth in paragraph 5
          below.

     b.   Cytyc shall provide to each LabCorp facility one additional ThinPrep
          2000 Processor when incremental utilization for Cytyc ThinPrep testing
          exceeds an average of *** tests per month over a consecutive three (3)
          month period of time. The charges for such additional instrumentation
          shall be included in the rates LabCorp shall pay Cytyc as more
          specifically set forth in paragraph 5 below. LabCorp shall provide
          Cytyc with monthly utilization reports for each LabCorp facility by
          the 20th day of the following month.

     c.   Cytyc and LabCorp agree to negotiate in good faith the placement of
          additional instrumentation in the event circumstances otherwise
          warrant in LabCorp's reasonable discretion but the utilization
          thresholds set forth in paragraph 3(b) above have not been met. Such
          circumstances may include, but shall not be limited to, anticipated
          additional capacity requirements due to new or enhanced LabCorp
          relationships in a particular market.

     d.   In the event LabCorp requires additional instrumentation beyond the
          requirements set forth in paragraph 3(b) and (c) during the term,
          LabCorp may purchase additional instrumentation at a cost of $***
          per instrument. Such instrumentation shall be owned by LabCorp.

     e.   During the term LabCorp may purchase ThinPrep 3000 Processors for $***
          per instrument.

6.   PURCHASE RIGHT: Upon termination of this Agreement, LabCorp shall have the
     right to purchase any ThinPrep 2000 Processor placed pursuant to paragraphs
     3(b) and (c) above at a cost of $*** per instrument. In the event LabCorp
     elects to purchase such instrumentation it shall provide Cytyc 15 days
     notice. Upon payment of the purchase price Cytyc shall convey to LabCorp
     all right, title, and interest to such instrumentation free and clear of
     all liens and encumbrances.

<PAGE>

7.   FEES: Effective January 1, 2002, and continuing throughout the remainder
     the term, Cytyc shall provide to LabCorp ThinPrep Pap Test Laboratory
     Supplies (1 X ThinPrep Pap Test microscope slide and 1 X ThinPrep Pap Test
     TransCyt Filter (one supply) for $*** each. Additional discounts shall be
     available based on the following schedule:

<TABLE>
<CAPTION>
Time Period                Laboratory Supplies Invoiced   Additional Discount Per Test
-----------                ----------------------------   ----------------------------
<S>                                 <C>                                <C>
Jan. 1, 2002-Dec. 31, 2002          Up to ***                          $***
                                    Excess over ***                    $***

Jan. 1, 2003-Dec. 31, 2003          Up to ***                          $***
                                    Excess over ***                    $***
                                    Excess over ***                    $***

Jan. 1, 2004-Dec. 31, 2004          Up to ***                          $***
                                    Excess over ***                    $***
                                    Excess over ***                    $***
</TABLE>

8.   COST PER BILLABLE TERMINATION: The Parties agree to transition from the
     cost per billable provisions of the original product addendum and terminate
     the cost per billable program effective January 1, 2002, as follows:

     a.   LabCorp will report monthly ThinPrep Pap Test usage to Cytyc for
          November 2001 and December 2001 no later than 5 business days
          following the end of fiscal year 2001.

     b.   Cytyc Corporation will invoice LabCorp for November and December
          ThinPrep Pap Test usage at the price of $*** per test.

     c.   LabCorp will provide to Cytyc during December 2001 a Consignment
          Inventory Payment for *** ThinPrep Pap Tests in LabCorp's possession
          at a price of *** for a total payment of $***

          On or about December 31, 2001, LabCorp will conduct a physical
          inventory to determine the total number of ThinPrep Pap Test
          Laboratory Supplies in inventory at all LabCorp facilities. LabCorp
          will pay Cytyc for the remaining inventory (December 31, 2001 Physical
          Inventory total MINUS *** pre-paid tests) at the rate of *** test.
          This remaining inventory will be paid to Cytyc in two equal
          installment payments, with the first installment due March 15, 2002,
          and the second installment due June 15, 2002.

9.   TRAINING

     Cytyc Corporation agrees to provide, at its expense, training at Cytyc's
     headquarters in Boxborough, Massachusetts for one cytopathologist and one
     cytotechnologist from each LabCorp facility that has not previously
     performed the ThinPrep Pap Test in that facility. Additional training of
     LabCorp laboratory personnel will be conducted by Cytyc Application
     Specialists. Such additional training shall be conducted at LabCorp
     facilities. Requests by LabCorp for additional on-site training can be
     scheduled through Cytyc Technical Service Department. This training shall
     be at no additional charge to LabCorp.

8. Except as specifically modified by this Amendment, the Agreement shall remain
unchanged and in full force and effect. In the event there is any conflict
between the terms of the original Agreement, Product and Equipment Addendum, the
terms of this Amendment shall control.

IN WITNESS WHEREOF, the parties have caused this Amendment to be executed in
their names as their official acts by their respective representatives, each of
whom is duly authorized to execute the same.

<PAGE>

Laboratory Corporation of America Holdings ("LabCorp")


BY: /s/ Illegible
    ----------------------------

TITLE: V.P./Director S&P

DATE: 12/20/01

WITNESS: Nevin Breedlove


CYTYC CORPORATION ("CYTYC")


BY: /s/ Daniel J. Levangie
    ----------------------------

TITLE: Chief Operating Officer

DATE: 12/18/01

WITNESS: Anne Marie Dodge

<PAGE>

                                 [LOGO] LabCorp

Laboratory Corporation of America(TM) Holdings
112 Orange Drive
Elon, North Carolina 27244
Telephone: 336-436-2857
FAX: 336-436-0565

Nevin Breedlove
National Director, Business Develeopment
Science & Technology

December 20, 2001

Dan Levangie
COO, Executive Vice President
Cytyc Corporation
85 Swanson Road
Boxborough, MA 01719

Dear Mr. Levangie:

This letter is to further clarify Paragraph 7, "FEES" as set forth in the
"Amendment to Master Agreement" dated December 20, 2001 by and between Cytyc
Corporation ("Cytyc") and Laboratory Corporation of America Holdings ("LabCorp")
which amends the Master Agreement and Equipment and Product Addenda entered into
between Cytyc and LabCorp dated the 1st day of January 2000 the ("Agreement").

It is understood that Cytyc will issue an additional discount in the form of a
check to LabCorp at the rates indicated in Paragraph 7 of the amendment
("Additional Discount Per Test") for all ThinPrep Pap Test Laboratory Supplies
invoiced to LabCorp in excess of the calendar year thresholds as described in
Paragraph 7 ("Time Period"). All ThinPrep Pap Test Laboratory Supplies invoiced
during the applicable Time Period will be applied to the aggregate annual
threshold. LabCorp will receive the Additional Discount beginning in the month
the threshold is exceeded and continuing through the remainder of the current
calendar year.

The attached example is solely for the purposes of illustration and in no way
represents actual ordering, charges, or additional discounts.

<PAGE>

EXAMPLE

------------------------------------------------------------------------
                                                     Price    Additional
                                        Additional    Per      Discount
          Laboratory            Price    Discount    Test         X
          Suppliers    Annual   Per        Per         X     Excess Over
Month      Involved    Total    Test      Tests      Tests    ***Tests
------------------------------------------------------------------------
        Kits   Tests
------------------------------------------------------------------------
Jan     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Feb     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Mar     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Apr     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
May     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Jun     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Jul     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Aug     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Sep     ***    ***      ***      ***       ***        ***
------------------------------------------------------------------------
Oct     ***    ***      ***      ***       ***        ***        ***
------------------------------------------------------------------------
Nov     ***    ***      ***      ***       ***        ***        ***
------------------------------------------------------------------------
Dec     ***    ***      ***      ***       ***        ***        ***
------------------------------------------------------------------------

LabCorp is invoiced for *** ThinPrep Pap Tests *** Kits x *** ThinPrep Pap tests
per Kit) for the month of October. The following illustrates the process by
which Cytyc and LabCorp will calculate fees and the additional discounts
described in Paragraph 7.

------------------------------------------------
STEP 1
------------------------------------------------
  ***    Tests
------------------------------------------------
X ***    Price Per Test
------------------------------------------------
$ ***    October Payment From LabCorp to Cytyc
------------------------------------------------

The invoice for * Tests enables LabCorp to exceed the * threshold and to qualify
for the Additional Discount described in Paragraph 7.

------------------------------------------------
STEP 2
------------------------------------------------
  ***      Annual Total Through October
------------------------------------------------
- ***      Threshold for Additional Discount
------------------------------------------------
  ***      Excess over*** Tests
------------------------------------------------

------------------------------------------------
STEP 3
------------------------------------------------
  ***      Excess over*** Tests
------------------------------------------------
X ***      Additional Discount
------------------------------------------------
  ***      October Payment from Cytyc to LabCorp
------------------------------------------------

The parties confirm their agreement to the above by executing below:

Laboratory Corporation of America         Cytyc Corporation


By: /s/ Illegible                         By: /s/ Daniel J. Levangie
    -----------------------------------       ----------------------------------

Title: V.P./Director S&P                  Title: Chief Operating Officer

Date:  12/20/01                           Date:  12/21/01
       --------------------------------          -------------------------------