Document:

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                                                                   EXHIBIT 10.41

                          FOURTH REPLACEMENT REVOLVING
                                 PROMISSORY NOTE

$2,000,000                                                   Rockville, Maryland
                                                               December 30, 1999

         FOR VALUE RECEIVED, BIORELIANCE CORPORATION, a corporation organized
and in good standing under the laws of the State of Delaware, successor in
interest to Microbiological Associates, Inc. (the "Company"), BIORELIANCE
TESTING AND DEVELOPMENT, INC., formerly known as MA BioServices, Inc., a
corporation organized and in good standing under the laws of the State of
Delaware ("MA BioServices"), BIORELIANCE MANUFACTURING, INC., formerly known as
Magenta Corporation, a corporation organized and in good standing under the laws
of the State of Delaware ("Magenta") and MAGENTA VIRAL PRODUCTION, INC., a
corporation organized and in good standing under the laws of the State of
Delaware ("Magenta Viral"; together with the Company, MA BioServices and
Magenta, each a "Borrower" and collectively, the "Borrowers"), jointly and
severally, promise to pay to the order of BANK OF AMERICA, N.A., successor to
NATIONSBANK, N.A., each a national banking association, its successors and
assigns (the "Lender"), the principal sum of TWO MILLION DOLLARS ($2,000,000)
(the "Principal Sum"), or so much thereof as has been or may be advanced or
readvanced to or for the account of the Borrowers pursuant to the terms and
conditions of the Loan Agreement (as hereinafter defined), together with
interest thereon at the rate or rates hereinafter provided, in accordance with
the following:

         1. INTEREST. Commencing as of the date hereof and continuing until
repayment in full of all sums due hereunder, the unpaid Principal Sum shall bear
interest at the LIBOR Rate (as hereinafter defined), plus the applicable LIBOR
Rate Additional Percentage (the "LIBOR Rate Option").

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                                                                   EXHIBIT 10.41

                  (a) For purposes hereof, the "LIBOR Rate Additional
Percentage" shall mean the percentages applicable to this Note in accordance
with the following:

                           (i) If the ratio of Funded Debt divided by EBITDA is
         equal to or greater than 2.75 to 1.0, the LIBOR Rate Additional
         Percentage shall be two percent (2.0%);

                           (ii) If the ratio of Funded Debt divided by EBITDA is
         less than 2.75 to 1.0, but equal to or greater than 2.0 to 1.0, the
         LIBOR Rate Additional Percentage shall be one and three quarters
         percent (1.75%);

                           (iii) If the ratio of Funded Debt divided by EBITDA
         is less than 2.0 to 1.0, but equal to or greater than 1.25 to 1.0 the
         LIBOR Rate Additional Percentage shall be one and one quarter percent
         (1.25%); and

                           (iv) If the ratio of Funded Debt divided by EBITDA is
         less than 1.25 to 1.0, the LIBOR Rate Additional Percentage shall be
         .85/100 percent (.85%)

                  (b) The initial LIBOR Rate Additional Percentage shall be two
percent (2.0%). Thereafter, the applicable LIBOR Rate Additional Percentage for
all Advances shall be calculated and adjusted quarterly, based on the quarterly
financial statements of the Borrowers required to be submitted to the Lender
pursuant to Section 5.1(c) of the Loan Agreement, commencing with the statements
for the quarter ending September 30, 1999. Such quarterly changes shall be
effective commencing five (5) Banking Days after submission by the Borrowers of
the required financial statements; it being understood, however, that, subject
to the provisions of the immediately following sentence, in the event the
quarterly financial statements are not submitted when due, the LIBOR Rate
Additional Percentage shall be two percent (2.00%), until such financial
statements are submitted as required, at which time, the LIBOR Rate Additional

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                                                                   EXHIBIT 10.41

Percentage (for the balance of the quarterly period) shall be determined as set
forth above. If such financial statements are not submitted when due, but are
received within thirty (30) days of when due, the Lender will return to the
Borrower any additional interest collected in excess of the amount that should
have otherwise been due hereunder based on the financial statements. For
purposes of this Note, "Funded Debt" and "EBITDA" shall each be determined based
on the consolidated quarterly financial statements of the Borrowers and shall
have the meanings set forth in the Loan Agreement.

                  (c) For purposes hereof, the "LIBOR Rate" shall mean a
fluctuating rate of interest equal to the one month rate of interest (rounded
upwards, if necessary to the nearest 1/100 of 1%) appearing on Telerate Page
3750 (or any successor page) as the one month London interbank offered rate for
deposits in Dollars at approximately 11:00 a.m. (London time) on the second
preceding business day as adjusted from time to time in Lender's sole discretion
for then applicable reserve requirements, deposit insurance assessment rates and
other regulatory costs. If for any reason such rate is not available, the term
"LIBOR Rate" shall mean the fluctuating rate of interest equal to the one month
rate of interest (rounded upwards, if necessary to the nearest 1/100 of 1%)
appearing on Reuters Screen LIBO Page as the one month London interbank offered
rate for deposits in Dollars at approximately 11:00 a.m. (London time) on the
second preceding business day, as adjusted from time to time in Lender's sole
discretion for then applicable reserve requirements, deposit insurance
assessment rates and other regulatory costs; provided, however, if more than one
rate is specified on Reuters Screen LIBO page, the applicable rate shall be the
arithmetic mean of all such rates. "Telerate Page 3750" means the British
Bankers Association Libor Rates (determined as of 11:00 a.m. London time) that
are published by Dow Jones Telerate, Inc.

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                                                                   EXHIBIT 10.41

                  (d) The Borrowers shall pay to the Lender, as additional
interest, the following sums, at the time and in the manner hereinafter set
forth:

                           (A) if, due to either: (i) the introduction of or any
change (including, without limitation, any change by way of imposition or
increase of reserve requirements) in or in the interpretation of any law or
regulation or (ii) the compliance by the Lender with any guideline or request
from any central bank or other governmental authority (whether or not having the
force of law), there shall be any increase in the cost to the Lender of agreeing
to make or making, funding or maintaining advances of all or a portion of the
Principal Sum, then the Borrowers shall from time to time, upon demand by the
Lender, pay to the Lender additional amounts to indemnify the Lender against any
such increased costs. A certificate as to the amount of such increased costs
submitted to the Borrowers by the Lender shall in the absence of manifest error
be conclusive. It shall be deemed, for purposes of computing any increased costs
pursuant to this Section, that (i) the making and maintaining of advances of the
Principal Sum which accrue interest based on the LIBOR Rate have been made by
the Lender from its office in London, England and (ii) the funding of each
Advance of the Principal Sum by the Lender which accrues interest based on the
LIBOR Rate has been made through the London Interbank Market. Such additional
cost shall be payable hereunder at the time and in the manner that interest is
payable hereunder for such costs incurred since the last interest payment;

                           (B) the Borrowers shall also pay to the Lender at the
time and in the manner that interest is payable hereunder for each advance, the
cost since the last interest payment date, as determined in good faith by the
Lender, of complying, in connection with such advance during such interest
period, with any reserve, special deposit or similar requirement (including but
not limited to reserve requirements under Federal Reserve Regulation D) imposed

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                                                                   EXHIBIT 10.41

or deemed applicable against any assets held by or deposits or accounts in or
with or credit extended by the Lender, or the office of the Lender in London,
England, by any United States governmental authority charged with the
administration of such requirements. Each notification as to the amount of such
cost, delivered to the Borrowers by the Lender shall, in the absence of manifest
error, be conclusive as to the amount of such cost. It shall be deemed for
purposes of computing cost pursuant to the above provision that the making and
maintaining of each advance which accrues interest based on the LIBOR Rate has
been made by the Lender through its office in London, England.

                  (e) In respect to any interest rate election hereunder and any
transactions contemplated hereby, the Borrowers authorize the Lender to accept,
rely upon, act upon and comply with, any verbal or written instructions,
requests, confirmations and orders of Capers W. McDonald, President and CEO, or
Patrick J. Spratt, CFO, or their successors in office, on behalf of the
Borrowers. The Borrowers acknowledge and agree that the transmission between the
Borrowers and the Lender of any such instructions, requests, confirmations and
orders involves the possibility of errors, omissions, mistakes and discrepancies
and agrees to adopt such internal measures and operational procedures to protect
its interests. By reason thereof, the Borrowers hereby assume all risk of loss
and responsibility for, releases and discharges the Lender from any and all
responsibility or liability for, and agrees to indemnify, reimburse on demand
and hold the Lender harmless from, any and all claims, actions, damages, losses,
liability and expenses by reason of, arising out of or in any way connected with
or related to, (i) the Lender's acceptance, reliance and actions upon,
compliance with or observation of any such instructions, requests, confirmations
or orders, and (ii) any such errors, omissions, mistakes and discrepancies,
except those caused by the Lender's gross negligence or willful misconduct.

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                                                                   EXHIBIT 10.41

                  (f) All interest payable under the terms of this Note shall
be calculated on the basis of a 360-day year and the actual number of days
elapsed.

         2.       PAYMENTS AND MATURITY. The unpaid Principal Sum, together with
interest thereon at the rate or rates provided above, shall be payable as
follows:

                  (a) Interest only on the unpaid Principal Sum shall be due and
payable monthly, commencing December 31, 1999 and on the last day of each month
thereafter to maturity; and

                  (b) Unless sooner paid, the unpaid Principal Sum, together
with interest accrued and unpaid thereon, shall be due and payable in full on
May 31, 2001.

         The fact that the balance hereunder may be reduced to zero from time to
time pursuant to the Loan Agreement will not affect the continuing validity of
this Note or the Loan Agreement, and the balance may be increased to the
Principal Sum after any such reduction to zero.

         3.      DEFAULT INTEREST. Upon the occurrence of an Event of Default
(as hereinafter defined), the unpaid Principal Sum shall bear interest
thereafter at  a rate five percent (5.0%) per annum in excess of the LIBOR Rate
until such event of Default is cured.

         4.      LATE CHARGES. If the Borrowers shall fail to make any payment
under the terms of this Note within fifteen (15) days after the date such
payment is due, the Borrowers shall pay to the Lender on demand a late charge
equal to three percent (3%) of such payment.

         5.      APPLICATION AND PLACE OF PAYMENTS. All payments, made on
account of this Note shall be applied first to the payment of any late charge
then due hereunder, second to the payment of accrued and unpaid interest then
due hereunder, and the remainder, if any, shall be applied to the unpaid
Principal Sum. All payments on account of this Note shall be paid in lawful
money of the United States of America in immediately available funds during
regular business

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                                                                   EXHIBIT 10.41

hours of the Lender at its principal office in Rockville, Maryland or at such
other times and places as the Lender may at any time and from time to time
designate in writing to the Borrowers.

         6. LOAN AGREEMENT AND OTHER LOAN DOCUMENTS. This Note is the "Restated
Line of Credit Replacement Note" described in that certain Second Amendment to
Amended and Restated Replacement Loan Agreement of even date herewith by and
among the Borrowers and the Lender, which amends that certain Amended and
Restated Replacement Loan Agreement dated October 31, 1997 by and among the
Borrower and the Lender (the Amended and Restated Replacement Loan Agreement, as
thereafter amended from time to time, is hereinafter called the "Loan
Agreement"). This Note increases, amends and restates in its entirety that
certain Third Replacement Revolving Promissory Note dated as of May 31, 1998 in
the maximum principal amount of One Million Dollars ($1,000,000) from the
Borrowers in favor of the Lender (as amended from time to time, the "Replacement
Note"). It is expressly agreed that the indebtedness evidenced by the
Replacement Note has not been extinguished or discharged hereby. The Borrowers
agree that the execution of this Agreement is not intended to and shall not
cause or result in a novation with respect to the Replacement Note. The
indebtedness evidenced by this Note is included within the meaning of the term
"Obligations" as defined in the Loan Agreement. The term "Loan Documents" as
used in this Note shall mean collectively this Note, the Loan Agreement and any
other instrument, agreement, or document previously, simultaneously, or
hereafter executed and delivered by the Borrowers and/or any other person,
singularly or jointly with any other person, evidencing, securing, guaranteeing,
or in connection with the Principal Sum, this Note and/or the Loan Agreement.
All capitalized terms used herein and not otherwise defined shall have the
meanings given to such terms in the Loan Agreement.

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                                                                   EXHIBIT 10.41

         7. EVENTS OF DEFAULT. The occurrence of any one or more of the
following events shall constitute an event of default (individually, an "Event
of Default" and collectively, the "Events of Default") under the terms of this
Note:

                  (a) The failure of the Borrowers to pay to the Lender when due
any and all amounts payable by the Borrowers to the Lender and such failure
remains uncured for five (5) days after written notice thereof; or

                  (b) The occurrence of an event of default (as defined therein)
under the terms and conditions of any of the other Loan Documents.

         8. REMEDIES. Upon the occurrence of an Event of Default, at the option
of the Lender, all amounts payable by the Borrowers to the Lender under the
terms of this Note shall immediately become due and payable by the Borrowers to
the Lender without notice to the Borrowers or any other person, and the Lender
shall have all of the rights, powers, and remedies available under the terms of
this Note, any of the other Loan Documents and all applicable laws. The
Borrowers and all endorsers, guarantors, and other parties who may now or in the
future be primarily or secondarily liable for the payment of the indebtedness
evidenced by this Note hereby severally waive presentment, protest and demand,
notice of protest, notice of demand and of dishonor and non-payment of this Note
and expressly agree that this Note or any payment hereunder may be extended from
time to time without in any way affecting the liability of the Borrowers,
guarantors and endorsers.

         Until such time as the Lender is not committed to extend further credit
to the Borrowers and all Obligations of the Borrowers to the Lender have been
indefeasibly paid in full in cash, and subject to and not in limitation of the
provisions set forth in the next following paragraph below, no Borrower shall
have any right of subrogation (whether contractual, arising under the

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                                                                   EXHIBIT 10.41

Bankruptcy Code or otherwise), reimbursement or contribution from any Borrower
or any guarantor, nor any right of recourse to its security for any of the debts
and obligations of any Borrower which are the subject of this Note. Except as
otherwise expressly permitted by the Loan Agreement, any and all present and
future debts and obligations of any Borrower to any other Borrower are hereby
subordinated to the full payment and performance of all present and future debts
and obligations to the Lender under this Note and the Loan Agreement and the
Loan Documents, provided, however, notwithstanding anything set forth in this
Note to the contrary, prior to the occurrence of a payment Default, the
Borrowers shall be permitted to make payments on account of any of such present
and future debts and obligations from time to time in accordance with the terms
thereof.

         Each Borrower further agrees that, if any payment made by any Borrower
or any other person is applied to this Note and is at any time annulled, set
aside, rescinded, invalidated, declared to be fraudulent or preferential or
otherwise required to be refunded or repaid, or the proceeds of any property
hereafter securing this Note is required to be returned by the Lender to any
Borrower, its estate, trustee, receiver or any other party, including, without
limitation, such Borrower, under any bankruptcy law, state or federal law,
common law or equitable cause, then, to the extent of such payment or repayment,
such Borrower's liability hereunder (and any lien, security interest or other
collateral securing such liability) shall be and remain in full force and
effect, as fully as if such payment had never been made, or, if prior thereto
any such lien, security interest or other collateral hereafter securing such
Borrower's liability hereunder shall have been released or terminated by virtue
of such cancellation or surrender, this Note (and such lien, security interest
or other collateral) shall be reinstated in full force and effect, and such
prior cancellation or surrender shall not diminish, release, discharge, impair
or otherwise affect the

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                                                                   EXHIBIT 10.41

obligations of such Borrower in respect of the amount of such payment (or any
lien, security interest or other collateral securing such obligation).

         The JOINT AND SEVERAL obligations of each Borrower under this Note
shall be absolute, irrevocable and unconditional and shall remain in full force
and effect until the outstanding principal of and interest on this Note and all
other Obligations or amounts due hereunder and under the Loan Agreement and the
Loan Documents shall have been indefeasibly paid in full in cash in accordance
with the terms thereof and this Note shall have been canceled.

         9. EXPENSES. The Borrowers, jointly and severally, promise to pay to
the Lender on demand by the Lender all reasonable costs and expenses incurred by
the Lender in connection with the collection and enforcement of this Note,
including, without limitation, reasonable attorneys' fees and expenses and all
court costs.

         10. NOTICES. Any notice, request, or demand to or upon the Borrowers or
the Lender shall be deemed to have been properly given or made when delivered in
accordance with Section 9.1 of the Loan Agreement.

         11. MISCELLANEOUS. Each right, power, and remedy of the Lender as
provided for in this Note or any of the other Loan Documents, or now or
hereafter existing under any applicable law or otherwise shall be cumulative and
concurrent and shall be in addition to every other right, power, or remedy
provided for in this Note or any of the other Loan Documents or now or hereafter
existing under any applicable law, and the exercise or beginning of the exercise
by the Lender of any one or more of such rights, powers, or remedies shall not
preclude the simultaneous or later exercise by the Lender of any or all such
other rights, powers, or remedies. No failure or delay by the Lender to insist
upon the strict performance of any term, condition, covenant, or agreement of
this Note or any of the other Loan Documents, or to exercise any

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                                                                   EXHIBIT 10.41

right, power, or remedy consequent upon a breach thereof, shall constitute a
waiver of any such term, condition, covenant, or agreement or of any such
breach, or preclude the Lender from exercising any such right, power, or remedy
at a later time or times. By accepting payment after the due date of any amount
payable under the terms of this Note, the Lender shall not be deemed to waive
the right either to require prompt payment when due of all other amounts payable
under the terms of this Note or to declare an Event of Default for the failure
to effect such prompt payment of any such other amount. No course of dealing or
conduct shall be effective to amend, modify, waive, release, or change any
provisions of this Note.

         12. PARTIAL INVALIDITY. In the event any provision of this Note (or any
part of any provision) is held by a court of competent jurisdiction to be
invalid, illegal, or unenforceable in any respect, such invalidity, illegality,
or unenforceability shall not affect any other provision (or remaining part of
the affected provision) of this Note; but this Note shall be construed as if
such invalid, illegal, or unenforceable provision (or part thereof) had not been
contained in this Note, but only to the extent it is invalid, illegal, or
unenforceable.

         13. CAPTIONS. The captions herein set forth are for convenience only
and shall not be deemed to define, limit, or describe the scope or intent of
this Note.

         14. APPLICABLE LAW. Each of the Borrowers acknowledges and agrees that
this Note shall be governed by the laws of the State of Maryland, even though
for the convenience and at the request of the Borrowers, this Note may be
executed elsewhere.

         15. ARBITRATION. ANY CONTROVERSY OR CLAIM BETWEEN OR AMONG THE PARTIES
HERETO INCLUDING BUT NOT LIMITED TO THOSE ARISING OUT OF THIS NOTE, THE LOAN
DOCUMENTS OR ANY RELATED INSTRUMENTS, AGREEMENTS OR DOCUMENTS, INCLUDING ANY
CLAIM BASED ON OR ARISING

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                                                                   EXHIBIT 10.41

FROM AN ALLEGED TORT, SHALL BE DETERMINED BY BINDING ARBITRATION IN ACCORDANCE
WITH THE FEDERAL ARBITRATION ACT (OR IF NOT APPLICABLE, THE APPLICABLE STATE
LAW), THE RULES OF PRACTICE AND PROCEDURE FOR ARBITRATION OF COMMERCIAL DISPUTES
OF ENDISPUTE, INC., D/B/A J.A.M.S./ENDISPUTE ("J.A.M.S.") AND THE "SPECIAL
RULES" SET FORTH BELOW. IN THE EVENT OF AN INCONSISTENCY, THE SPECIAL RULES
SHALL CONTROL. JUDGMENT UPON ANY ARBITRATION AWARD MAY BE ENTERED IN ANY COURT
HAVING JURISDICTION. ANY PARTY TO THIS NOTE, AGREEMENT OR DOCUMENT MAY BRING ANY
ACTION, INCLUDING A SUMMARY OR EXPEDITED PROCEEDING, TO COMPEL ARBITRATION OF
ANY CONTROVERSY OR CLAIM TO WHICH THIS NOTE, AGREEMENT OR DOCUMENT RELATES IN
ANY COURT HAVING JURISDICTION OVER SUCH ACTION.

         (A) SPECIAL RULES. THE ARBITRATION SHALL BE CONDUCTED IN MONTGOMERY
COUNTY, MARYLAND AND ADMINISTERED BY J.A.M.S. WHO WILL APPOINT AN ARBITRATOR. IF
J.A.M.S. IS UNABLE OR LEGALLY PRECLUDED FROM ADMINISTERING THE ARBITRATION, THEN
THE AMERICAN ARBITRATION ASSOCIATION WILL SERVE. ALL ARBITRATION HEARINGS WILL
BE COMMENCED WITHIN NINETY (90) DAYS OF THE DEMAND FOR ARBITRATION; FURTHER, THE
ARBITRATOR SHALL ONLY, UPON A SHOWING OF CAUSE, BE PERMITTED TO EXTEND THE
COMMENCING OF SUCH HEARING FOR AN ADDITIONAL SIXTY (60) DAYS.

         (B) RESERVATION OF RIGHTS. NOTHING IN THIS NOTE, AGREEMENT OR DOCUMENT
SHALL BE DEEMED TO: (I) LIMIT THE APPLICABILITY OF ANY

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                                                                   EXHIBIT 10.41

OTHERWISE APPLICABLE STATUTES OF LIMITATION OR REPOSE AND ANY WAIVERS CONTAINED
IN THIS NOTE, AGREEMENT OR DOCUMENT; OR (II) BE A WAIVER BY THE LENDER OF THE
PROTECTION AFFORDED TO IT BY 12 U.S.C. Section 91 OR ANY SUBSTANTIALLY
EQUIVALENT STATE LAW; OR (III) LIMIT THE RIGHT OF THE LENDER: (A) TO EXERCISE
SELF HELP REMEDIES ( BUT NOT INCLUDING SETOFF), OR (B) TO FORECLOSE AGAINST ANY
REAL OR PERSONAL PROPERTY COLLATERAL, OR (C) TO OBTAIN FROM A COURT PROVISIONAL
OR ANCILLARY REMEDIES SUCH AS (BUT NOT LIMITED TO) INJUNCTIVE RELIEF, WRIT OF
POSSESSION OR THE APPOINTMENT OF A RECEIVER. THE LENDER MAY EXERCISE SUCH SELF
HELP RIGHTS, FORECLOSE UPON SUCH PROPERTY, OR OBTAIN SUCH PROVISIONAL OR
ANCILLARY REMEDIES BEFORE, DURING OR AFTER THE PENDENCY OF ANY ARBITRATION
PROCEEDING BROUGHT PURSUANT TO THIS NOTE, AGREEMENT OR DOCUMENT. NEITHER THE
EXERCISE OF SELF HELP REMEDIES NOR THE INSTITUTION OR MAINTENANCE OF ANY ACTION
FOR FORECLOSURE OR FOR PROVISIONAL OR ANCILLARY REMEDIES SHALL CONSTITUTE A
WAIVER OF THE RIGHT OF ANY PARTY, INCLUDING THE CLAIMANT IN SUCH ACTION, TO
ARBITRATE THE MERITS OF THE CONTROVERSY OR CLAIM OCCASIONING RESORT TO SUCH
REMEDIES.

                    [SIGNATURES BEGIN ON THE FOLLOWING PAGE]

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                                                                   EXHIBIT 10.41

         IN WITNESS WHEREOF, the Borrowers have caused this Note to be executed
under seal by their duly authorized officers as of the date first written above.

<TABLE>
<S>                                                  <C>
WITNESS/ATTEST:                                      BIORELIANCE CORPORATION

                                                     By:                             (SEAL)
------------------------------                          -----------------------------
                                                        Name:
                                                        Title:

WITNESS/ATTEST:                                      BIORELIANCE TESTING AND
                                                     DEVELOPMENT, INC.

                                                     By:                             (SEAL)
------------------------------                          -----------------------------
                                                        Name:
                                                        Title:

WITNESS/ATTEST:                                      BIORELIANCE MANUFACTURING, INC.

                                                     By:                             (SEAL)
------------------------------                          -----------------------------
                                                        Name:
                                                        Title:

WITNESS/ATTEST:                                      MAGENTA VIRAL PRODUCTION, INC.

                                                     By:                             (SEAL)
------------------------------                          -----------------------------
                                                        Name:
                                                        Title:
</TABLE>

                                       14<PAGE>   1
                                                                   EXHIBIT 10.42

                              EMPLOYMENT AGREEMENT
                                     BETWEEN
                             BIORELIANCE CORPORATION
                                       AND
                             JOHN E. McENTIRE, Ph.D.

         THIS AGREEMENT, effective the 2nd day of December, 1999, by and between
BioReliance Corporation, a Delaware corporation, with principal offices located
at 14920 Broschart Road, Rockville, MD 20850, and all of its subsidiary
companies and its successors or assigns (the "Corporation") and John E.
McEntire, Ph.D. (the "Executive").

                             Preliminary Statements

         WHEREAS, the Executive is currently employed by the Corporation;

         WHEREAS, the parties desire to provide for the continued employment of
the Executive by the Corporation on the terms and conditions set forth in this
Agreement; and

                        Terms and Conditions of Agreement

         NOW THEREFORE, in consideration of the mutual promises and agreements
set forth in this Agreement, the adequacy of which are acknowledged, and with
the intent to be bound hereby, the Corporation and the Executive agree as
follows:

A.        POSITION

         The Executive will be employed as Vice President, U.S. Testing and
Development of the Corporation commencing with this Agreement. The Executive
shall continue as Vice President, U.S. Testing and Development, or such other
senior management position as may be determined by the Corporation from time to
time, through the remainder of the Term.

B.  DUTIES

         As Vice President, U.S. Testing and Development, the Executive shall
perform such duties as may be assigned to him from time to time by the President
and Chief Executive Officer of the Corporation (the "CEO"), including, but not
limited to: developing and documenting novel or typical testing or development
programs, procedures, methodologies and the like; engaging clients for the
Corporation's testing and development services; designing major projects;
writing project plans; closing key proposals; directing projects of significant
scale and scope; directing complex technical activities; solving challenging
technical, regulatory

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                                                                   EXHIBIT 10.42

and service problems; building client relationships; and anticipating follow-on
client engagements.

C.       TERM

          The terms and conditions of this Employment Agreement will cover a
period beginning as of the date hereof and ending on January 1, 2000 (the
"Term"), unless otherwise terminated as provided in Section E below. During the
Term of this Agreement, the parties acknowledge that the Executive's employment
is not "at will" employment, and the Corporation's obligation to pay the
Executive the compensation described in Section E of this Agreement shall exist
regardless of any decision by the Corporation to terminate the Executive's
employment for any reason (other than a termination for cause) prior to the
expiration of the Term. At the end of the Term of this Agreement, the
Executive's employment status shall terminate. The terms and conditions
contained in Section E of this Agreement will expire at the end of the Term.

D.       EXTENSION OF TERM

         The Term of this Agreement may be extended in three (3) month
increments upon mutual, written agreement of both parties.

E.        COMPENSATION AND BENEFITS

                  (i)     Base Salary

                  The Executive's annual base salary will be One Hundred and
         Eighty-Five Thousand Dollars ($185,000), payable on the Corporation's
         regular bi-weekly payroll basis. The Executive shall receive only that
         portion of the base that will become due during the Term, and not the
         total annual base salary.

                  (ii)      Bonus

                  If the Executive remains in the employ of the Corporation
         through January 1, 2000, the Executive shall be paid a bonus of Ten
         Thousand Dollars ($10,000), less applicable withholdings and deductions
         (if any), without appraisal, on January 31, 2000. The Corporation will
         be obligated to pay the Executive this bonus as long as the Executive
         (a) does not resign from the Corporation before January 1, 2000 and (b)
         is not terminated for Cause (as hereinafter defined) on or before
         January 1, 2000.

                  (iii)     Incentive Stock Options

                  As an inducement to remain in the employ of the Corporation
         and as an incentive to build the Corporation's value, if the Executive
         remains in the employ of the Corporation through January 1, 2000, the
         Corporation will fully vest any Incentive Stock Options previously
         granted as of January 1, 2000, and the

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                                                                   EXHIBIT 10.42

         Executive will retain all rights and obligations pertaining thereto in
         accordance with the terms of the applicable plan. The Corporation will
         be obligated to fully vest any Incentive Stock Options previously
         granted as long as the Executive (a) does not resign from the
         Corporation before January 1, 2000 and (b) is not terminated for Cause
         (as hereinafter defined) on or before January 1, 2000.

                  (iv)      Other Provisions

                  The Corporation will provide such medical and other insurance
         coverage to the Executive as the Corporation makes available to all
         employees generally from time to time. Eligibility to extend group
         health coverage beyond the Term for the Executive or any dependants may
         be exercised by signing the applicable COBRA agreement.

                  The Executive will receive the Corporation's standard
         vacation, sick time and personal holiday benefits during the Term. The
         Executive will continue to accrue Paid Personal Leave (PPL) through the
         Term of this Agreement, and any unused PPL will be due to the Executive
         upon termination of employment.

                  The Corporation will provide the Executive with appropriate
         office space as it deems necessary, and will provide telephone,
         computer and email access as required to perform his duties during the
         Term of this Agreement.

F.       TERMINATION COMPENSATION AND BENEFITS

         In the event that during the Term of this Agreement, the Executive's
employment with the Corporation is involuntarily terminated by the Corporation
other than for Cause or because of the Executive's death or substantial
inability to work, the Corporation will pay the Executive a lump sum payment
equal to all amounts that would have otherwise become due hereunder, including
without limitation the Bonus described in Section E (ii) and the Corporation
will vest the incentive stock options in accordance with Section E (iii) hereof.

         For a period of six (6) months after such termination, the Corporation
will also continue to make available the same health and dental (but no other)
benefits made available to Corporation employees generally at a cost equal to
the cost the Executive would have paid if he had continued to be an employee of
the Corporation. In the event the Executive becomes employed at any time during
the six (6) month continuance period, all remaining health and dental benefits
shall terminate as of date of hire by the Executive's new employer.

         If the Executive terminates his employment prior to the end of the
Term, the Corporation shall have no further obligations under Sections E or F
hereof after the effective date of termination.

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                                                                   EXHIBIT 10.42

         As used in this Agreement, "Cause" shall mean that the Executive (a)
committed a material act or material acts of personal dishonesty intended to
result in the Executive's personal enrichment at the expense of the Corporation,
and which constitute(s) fraud, grand larceny or any felonious act, (b) failed or
refused to perform the Executive's material duties and obligations as an
employee of the Corporation (other than due to disability or reasons beyond the
Executive's reasonable control) if such failure or approval is not remedied
within a reasonable period of time following the Executive's receipt of notice
thereof.

G.    RELEASE

      The Executive acknowledges that absent this Agreement, he has no right
or entitlement to any separation payment and benefits, or to a separation
allowance in any particular amount. In consideration of the payment to him of
the monies and other benefits set forth herein, the Executive, on behalf of
himself and his heirs, executors, administrators and assigns, hereby releases
and discharges BioReliance, its agents, employees, successors, assigns,
affiliates, subsidiaries, officers, and directors, and each of them, from any
and all real or pretended claims, demands, rights, liabilities, damages,
injuries or causes of action whatsoever, known or unknown, including but not
limited to, claims and demands relating to salary, compensation, pension or
retirement plans (except as to rights which already may have vested, which
rights are specifically reserved hereunder), bonuses, incentive compensation,
commissions or any other form of compensation or perquisite, personal injury,
bodily injury, defamation, unlawful interference with contract rights or
business advantage, and any claims under the Age Discrimination in Employment
Act of 1967, or under any other federal, state, or local law prohibiting
employment discrimination (including, but not limited to, the Executive's right
to make a claim in his own right or through a suit brought by a third party on
his behalf), and any or all claims which he ever had or now has directly or
indirectly, arising out of his employment relationship with BioReliance or the
ending of that employment relationship with BioReliance, and all said rights,
actions, claims, demands, judgments, and executions are hereby satisfied in
full, terminated and forever discharged.

         By granting this Release, the Executive acknowledges that this
Agreement in no way constitutes an admission by BioReliance of any violation of
law, breach of contract or any wrongdoing whatsoever towards him.

         Upon termination of the Executive's employment, and as a condition to
the initiation of a Professional Services Agreement, if any, the Executive will
be requested to sign a release covering the period from the date hereof until
January 1, 2000.

H.      CONFIDENTIALITY AND NONCOMPETITION

         By signing below, the Executive acknowledges his ongoing and continuing
obligation to abide by the Confidentiality, Trade Secrets and Noncompetition
Agreement that he executed on June 23, 1998 ("Trade Secrets Agreement"), and to
keep secret or confidential, and not to utilize in any matter or disclose to
third parties, any proprietary

                                       4
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                                                                   EXHIBIT 10.42

and confidential information of the Corporation, which may have been made
available to him or came into his possession during the period of his employment
with the Corporation, nor will the Executive compete with the Corporation nor
solicit its (i) current or prospective employees for employment elsewhere or
(ii) current or prospective customers. The Corporation and the Executive
acknowledge that the noncompetion provisions of Section 4 (i) of the Trade
Secrets Agreement are not intended to prevent the Executive from seeking or
accepting employment from a customer or client of BioReliance provided that the
customer or client does not provide competing services to third parties. The
provisions of Section 4 (ii) and 4 (iii) of the Trade Secrets Agreement shall
apply in all events.

         The Executive also agrees that, during and after the Term, he shall not
make any defamatory or disparaging comments about the Corporation, its agents,
employees, successors, assigns, corporate parent, subsidiaries, affiliates,
officers, or directors to third parties, or to former, present, or prospective
customers, clients, vendors, business associates or anyone else in the industry,
and shall not unlawfully interfere with the business advantage or contracts of
the Corporation, its successors, assigns, corporate parent, subsidiaries, and
affiliates. During and after the Term, the Corporation agrees that the CEO and
the Vice Presidents of the Corporation shall not make any defamatory or
disparaging comments about the Executive.

I.       ACKNOWLEDGEMENT

         By signing below, the Executive acknowledges that he has read the
foregoing Release; that he has had a right to consult an attorney, and has been
encouraged by BioReliance to review this Agreement with an attorney; that he has
been given a period of not less than twenty-one (21) days in which to consider
this Agreement; that he understands it; and that he accepts and agrees to all of
the provisions contained herein. The Executive understands that this Agreement
sets forth the entire understanding of the parties, and he acknowledges that he
has not relied upon any other representations or promises in entering into this
Agreement.

J.       REVOCATION

         This Agreement may be revoked by the Executive at any time during the
seven (7) days immediately following his execution of the Agreement, after which
time the Agreement shall be irrevocable and enforceable in any court of
competent jurisdiction. In the event that the Executive exercises his right to
revoke during the seven-day period, any sums previously paid pursuant to the
terms of this Agreement shall be returned to BioReliance.

K.       PROFESSIONAL SERVICES

         During the twelve (12) month period following the expiration of the
Term hereof, the Executive may provide such professional services to the
Corporation as agreed and set forth in a Professional Services Agreement. These
services will be for the purposes

                                       5
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                                                                   EXHIBIT 10.42

set forth in the Professional Services Agreement as well as for the purpose of
accomplishing a smooth transition of obligations from the Executive to the
Corporation's Vice President, Biosafety Testing Services, and for facilitating
the Corporation's development of its analytical services business.

L.       SURVIVAL

         Except for the terms and conditions set forth above in Section E, the
terms and conditions of this Agreement, including without limitation the terms
and conditions set forth above in Section H regarding Confidentiality, Trade
Secrets and Noncompetition, will remain in effect after the end of the Term.

M.       ASSIGNABILITY

         Except by will or by the laws of descent and distribution, neither this
Agreement nor any right or interest hereunder shall be assignable or
transferable by the Executive or by the Executive's beneficiaries or legal
representatives. This Agreement shall inure to the benefit of and be enforceable
by the Executive's legal personal representative.

N.       GOVERNING LAW

         This agreement shall be construed and governed by the laws of the State
of Maryland without regard to its choice of law provisions.

O.       SEVERABILITY

         The provisions of this Agreement shall be deemed severable, and the
invalidity or unenforceability of any provision shall not affect the validity or
enforceability of the other provisions hereof.

P.       ENTIRE AGREEMENT

         This Agreement constitutes the entire Agreement between the Corporation
and the Executive and supersedes all prior agreements, offers, terms or
conditions regarding the Executive's employment, except for the Confidentiality,
Trade Secrets and Noncompetition Agreement, which will survive.

Q.       WAIVER

         The Executive acknowledges, absent this Agreement, the Executive has no
right or entitlement to any severance payment and benefit, or to a separate
allowance in any particular amount. For the consideration set forth in Section E
(ii) and (iii) and Section F hereof, the adequacy of which is hereby
acknowledged, except for breach of this Agreement by the Corporation, the
Executive hereby remises, releases and forever discharges and quitclaims onto
the Corporation and its officers, directors, shareholders, employees, agents and
representatives of and from any and all debts, actions, causes of

                                       6
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                                                                   EXHIBIT 10.42

action, suits, accounts, covenants, contracts, agreements, damages, and any and
all claims, demands and liabilities whatsoever of every name and nature, both in
Law and in Equity (collectively referred to therein as "Claims"), which the
Executive now has or ever had from the beginning of time.

R.       NO CONFLICTS OF INTEREST

         By signing this Agreement, the Executive represents that he is not
subject to any restrictions, particularly, but without limitation, in connection
with any previous employment, which prevents the Executive from entering into
and performing his obligations under this Agreement or which materially and
adversely affect (or may in the future, so far as the Executive can reasonably
foresee, materially and adversely affect), the Executive's right to participate
in the affairs of the Corporation.

S.       ARBITRATION

         Any claim or controversy relating to or arising out of this Agreement
shall be resolved exclusively by arbitration in accordance with the commercial
rules then obtaining of the American Arbitration Association. The arbitration
shall take place in Montgomery County, Maryland.

T.       PROOF OF CITIZENSHIP AND ABILITY TO WORK

         This Agreement is contingent on the Executive providing the
Corporation, if not previously provided, with proof of U.S. citizenship or alien
work permission, as required by federal law.

BioReliance Corporation

By: s/Capers W. McDonald                   By: s/John E. McEntire
    ------------------------------             ---------------------------------
Name:  Capers W. McDonald                  Name: John E. McEntire
Title: President and CEO
Date:  December 2, 1999                    Date: December 14, 1999

                                       7

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