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                                                                   Exhibit 10(M)


                             EMPLOYMENT AGREEMENT
                             --------------------


      AGREEMENT by and between LIFE TECHNOLOGIES, INC., a Delaware Corporation
(the "Company"), and John E. Leffler (the "Executive"), dated as of the 11th day
of April, 1995.

      The Board of Directors of the Company (the "Board"), has determined that
it is in the best interests of the Company and its shareholders to assure that
the Company will have the continued dedication of the Executive, notwithstanding
the possibility, threat or occurrence of a Change of Control (as defined below).
The Board believes it is imperative to diminish the inevitable distraction of
the Executive by virtue of the personal uncertainties and risks created by a
pending or threatened Change of Control and to encourage the Executive's full
attention and dedication to the Company currently and in the event of any
threatened or pending Change of Control, and to provide the Executive with
compensation and benefits arrangements upon a Change of Control which ensure
that the compensation and benefits expectations of the Executive will be
satisfied and which are competitive with those of other corporations.
Therefore, in order to accomplish these objectives, the Board has caused the
Company to enter into this Agreement.

      NOW, THEREFORE, IT IS HEREBY AGREED AS FOLLOWS:

      1.  Certain Definitions
          -------------------

      (a) The "effective Date" shall be the first date during the "Change of
Control Period" (as defined in Section 1(b)) on which a Change of Control
occurs.

      (b)  The "Change of Control Period" is the period commencing on the date
hereof and ending on the second anniversary of such date; provided, however,
that commencing on the date one year after the date hereof, and on each annual
anniversary of such date (such date and each annual anniversary thereof is
hereinafter referred to as the "Renewal Date"), the Change of Control Period
shall be automatically extended so as to terminate two years from such Renewal
Date, unless at least 60 days prior to the Renewal Date the Company shall give
notice to the Executive that the Change of Control Period shall not be so
extended.

      2.  Change of Control.  For the purpose of this Agreement;
          -----------------                                     

      (i) a "Change of Control" shall mean:

      (a) The acquisition, other than from the Company, by any individual,
entity or group (within the meaning of Section 13(d) (3) or 14(d) (2) of the
Securities Exchange Act of 1934, as amended (the "Exchange Act")) of beneficial
ownership (within the meaning of Rule 13d-3 under the Exchange Act) of 50% or
more of either the then outstanding shares of common stock of the Company (the
"Outstanding Company Common Stock") or the combined voting power of the then
outstanding voting securities of the Company entitled to vote generally in the
election of directors (the "Outstanding Company Voting Securities"), provided,
however, that any acquisition approved by a majority of the Incumbent Board (as
hereinafter defined), including a majority of the members of the Incumbent Board
who are not Dexter-related Directors (as 

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hereinafter defined) or any acquisition by the Company, the Dexter Corporation
("Dexter") or any of their subsidiaries, or by any employee benefit plan (or
related trust) sponsored or maintained by the Company, Dexter or any of their
subsidiaries, or by any corporation with respect to which, following such
acquisition, more than 50% of, respectively, the then outstanding shares of
common stock of such corporation and the combined voting power of the then
outstanding share of common stock of such corporation and the combined voting
power of the then outstanding voting securities of such corporation entitled to
vote generally in the election of directors is then beneficially owned, directly
or indirectly, by all/or substantially all the individuals and entities who were
the beneficial owners, respectively, of the Outstanding Company Common Stock and
Outstanding Company Voting Securities immediately prior to such acquisition in
substantially the same proportion as their ownership, immediately prior to such
acquisition, of the Outstanding Company Common Stock and Outstanding Company
Voting Securities, as the case may be, shall not constitute a Change of Control;
or

      (b) Individuals who as of April 19, 1989, constitute the Board of
Directors of the Company (the "Incumbent Board") cease for any reason to
constitute at least a majority of the Board of Directors of the Company,
provided that any individual becoming a director subsequent to April 19, 1989,
whose election, or nomination for election, by the Company's shareholders was
approved by a vote of at least a majority of the directors then comprising the
Incumbent Board, including a majority of the members of the Incumbent Board who
are not Dexter-related Directors, shall be considered as though such individual
were a member of the Incumbent Board, but excluding, for this purpose, any such
individual whose initial assumption of office is in connection with an actual or
threatened election contest (as such terms are use in Rule 14a-11 of the
Regulation 14A promulgated under the Exchange Act) relating to the election of
Directors of the Company; or

      (ii) at any time when either (x) Dexter is the beneficial owner (within
the meaning of Rule 13d-3 under the Exchange Act) of 20% or more of either the
Outstanding Company Common Stock or the Outstanding Company Voting Securities
and at least half of the directors of the Company are Dexter-related Directors
(as hereinafter defined), or (y) Dexter is the beneficial owner (within the
meaning of Rule 13d-3 under the Exchange Act) of 40% or more of either the
Outstanding Company Common Stock or the Outstanding Company Voting Securities
and there shall after any of the events set forth in the following clauses (a),
(b) or (c) be an increase in the percentage of the directors of the Company who
are Dexter-related Directors, then, in addition to the provisions of clause (i)
above, "Change of Control" shall mean:

          (a) The acquisition, other than from Dexter, by any individual, entity
or group (within the meaning of Section 13(d) (3) or 14(d) (2) of the Exchange
Act) of beneficial ownership (within the meaning of Rule 13d-3 under the
Exchange Act) of 20% or more of either the then outstanding shares of Common
Stock of Dexter (the "Outstanding Dexter Common Stock") or the combined voting
power of the then outstanding voting securities of Dexter entitled to vote
generally in the election of directors (the "Outstanding Dexter Voting
Securities"), provided, however, that any acquisition by the Company, Dexter or
any of their subsidiaries, or by any employee benefit plan (or related trust)
sponsored or maintained by the Company, Dexter or any of their subsidiaries, or
by any corporation with respect to which, following such acquisition, more than
50% of, respectively, the then outstanding shares of 

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common stock of such corporation and the combined voting power of the then
outstanding voting securities of such corporation entitled to vote generally in
the election of directors is then beneficially owned, directly or indirectly, by
all or substantially all the individuals and entities who were the beneficial
owners, respectively, of the Outstanding Dexter Common Stock and Outstanding
Dexter Voting Securities immediately prior to such acquisition in substantially
the same proportion as their ownership, immediately prior to such acquisition,
of the Outstanding Dexter Common Stock and Outstanding Dexter Voting Securities,
as the case may be, shall not constitute a Change of Control; or

          (b) Individuals who, as of January 1, 1989, constitute the Board of
Directors of Dexter (the "Dexter Incumbent Board") cease for any reason to
constitute at least a majority of the Board of Directors of Dexter, provided
that any individual becoming a director subsequent to January 1, 1989, whose
election, or nomination for election, by Dexter's shareholders was approved by a
vote of at least a majority of the directors then comprising the Dexter
Incumbent Board shall be considered as though such individual were a member of
the Dexter Incumbent Board, but excluding, for this purpose, any such individual
whose initial assumption of office is in connection with an actual or threatened
election contest (as such terms are used in Rule 14a-11 of Regulation 14A
promulgated under the Exchange Act) relating to the election of the Directors of
Dexter; or

          (c) Approval by the stockholders of Dexter of a complete liquidation
or dissolution of Dexter or of the sale or other disposition of all or
substantially all of the assets of Dexter, or of a reorganization, merger or
consolidation, in each case, with respect to which all or substantially all of
the individuals and entities who were the respective beneficial owners of the
Outstanding Dexter Common Stock and Outstanding Dexter Voting Securities
immediately prior to such reorganization, merger or consolidation do not,
following such reorganization, merger or consolidation, beneficially own,
directly or indirectly, more than 50% of, respectively, the then outstanding
shares of common stock and the combined voting power of the then outstanding
voting securities entitled to vote generally in the election of directors, as
the case may be, of the corporation resulting from such reorganization, merger
or consolidation;

      For purposes of this Agreement, a "Dexter-related Director" shall mean any
director of the Company who is or during the prior 10 years has been an officer,
director, employee or 5% or greater shareholder of Dexter or any of its
subsidiaries (other than the Company and its subsidiaries) or an officer,
director, partner, employee or 5% or greater shareholder of any law firm,
investment bank or other business organization that has been retained by Dexter
or any of its subsidiaries (other than the Company and its subsidiaries) to
provide services for an aggregate renumeration in any year of in excess of 5% of
the revenues of such law firm, investment bank or other business organization or
is otherwise controlling, controlled by or under common control with Dexter.

      3.  Employment Period.  The Company hereby agrees to continue the
          -----------------                                            
Executive in its employ, and the Executive hereby agrees to remain in the employ
of the Company, for the period commencing on the Effective Date and ending at
the end of the 12th month following the Effective Date (the "Employment
               ----                                                    
Period").

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    4.  Terms of Employment.
          ------------------- 

      (a) Position and Duties.
          ------------------- 

          (i)  During the Employment Period, (A) the Executive's position
(including status, offices, titles and reporting requirements), authority,
duties and responsibilities shall be at least commensurate in all material
respects with the most significant of those held, exercised and assigned at any
time during the 90-day period immediately preceding the Effective Date and (B)
the Executive's services shall be performed at the location where the Executive
was employed immediately preceding the Effective Date or any office or location
less than 25 miles from such location.

          (ii) During the Employment Period, and excluding any periods of
vacation and sick leave to which the Executive is entitled, the Executive agrees
to devote reasonable attention and time during normal business hours to the
business and affairs of the Company ad, to the extent necessary to discharge the
responsibilities assigned to the Executive hereunder, to use the Executive's
reasonable best efforts to perform faithfully and efficiently such
responsibilities.  During the Employment Period it shall not be a violation of
this Agreement for the Executive to (A) serve on corporate, civic or charitable
boards or committees, (B) deliver lectures, fulfill speaking engagements or
teach at educational institutions and (C) manage personal investments, so long
as such activities do not significantly interfere with the performance of the
Executive's responsibilities as an employee of the Company in accordance with
this Agreement.  It is expressly understood and agreed that to the extent that
any such activities have been conducted by the Executive prior to the Effective
Date, the continued conduct of such activities (or the conduct of activities
similar in nature and scope thereto) subsequent to the Effective Date shall not
thereafter be deemed to interfere with the performance of the Executive's
responsibilities to the Company.

      (b) Compensation.
          ------------ 

          (i) Base Salary.  During the Employment Period, the Executive shall
              -----------                                                    
receive an annual base salary ("Annual Base Salary"), which shall be paid at a
monthly rate, at least equal to twelve times the highest monthly base salary
paid or payable to the Executive by the Company and its affiliated companies in
respect of the twelve month period immediately preceding the month in which the
Effective Date occurs.  During the Employment Period, the Annual Base Salary
shall be reviewed at least annually and shall be increased at any time and from
time to time as shall be substantially consistent with increases in base salary
generally awarded in the ordinary course of business to other peer executives of
the Company and its affiliated companies.  Any increase in Annual Base Salary
shall not serve to limit or reduce any other obligation to the Executive under
this Agreement.  Annual Base Salary shall not be reduced after any such increase
and the term Annual Base Salary as utilized in this Agreement shall refer to the
Annual Base Salary as so increased.  As used in this Agreement, the term
"affiliated companies" includes any company controlled by, controlling or under
common control with the Company.

          (ii) Annual Bonus.  In addition to Annual Base Salary, the Executive
               ------------                                                   
shall be awarded, for each fiscal year during the Employment Period, 

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an annual bonus (the "Annual Bonus") in cash at least equal to either (A) the
average annualized (for any fiscal year consisting of less than twelve full
months or with respect to which the Executive has been employed by the Company
for less than twelve full months) bonus paid, or payable but for any deferral to
the Executive by the Company and its affiliated companies under the Company's
deferred compensation arrangements, in respect of the three fiscal years
immediately preceding the fiscal year in which the Effective Date occurs, or
(B), in the event the annual bonus paid, or payable but for any deferral to the
Executive by the Company and its affiliated companies under the Company's
deferred compensation arrangement, in respect of the fiscal year immediately
preceding the fiscal year in which the Effective Date occurs was based upon a
formula or plan in which the Executive participated, then such Annual Bonus
shall be at least equal to the bonus which would be payable based on such
formula or plan had the Executive's participation therein and level of
participation remained in effect following the Effective Date. Each such Annual
Bonus shall be paid no later than the end of the third month of the fiscal year
next following the fiscal year for which the Annual Bonus, is awarded, unless
the Executive shall elect to defer the receipt of such Annual Bonus.

          (iii) Incentive, Savings and Retirement Plans.  In addition to Annual
                ---------------------------------------                        
Base Salary and Annual Bonus payable as hereinabove provided, the Executive
shall be entitled to participate during the Employment Period in all incentive,
savings and retirement plans, practices, policies and programs generally
applicable to other peer executives of the Company and its affiliated companies,
but in no event shall such plans, practices, policies and programs provide the
Executive with incentive opportunities (measured with respect to both regular
and special incentive opportunities), savings opportunities and retirement
benefits opportunities, in each case, less favorable, in the aggregate, than the
most favorable of those provided by the Company and its affiliated companies for
the Executive under such plans, practices, policies and programs as in effect at
any time during the 90-day period immediately preceding the Effective Date.

          (iv) Welfare Benefit Plans.  During the Employment Period, the
               ---------------------                                    
Executive and/or the Executive's family, as the case may be, shall be eligible
for participation in and shall receive all benefits under welfare benefit plans,
practices, policies and programs provided by the Company and its affiliated
companies (including, without limitation, medical, prescription, dental,
disability, salary continuance, employee life, group life, accidental death and
travel accident insurance plans and programs) to the extent generally applicable
to other peer executives of the Company and its affiliated companies, but in no
event shall such plans, practices, policies and programs provide benefits which
are less favorable, in the aggregate, than the most favorable of such plans,
practices, policies and programs in effect for the Executive at any time during
the 90-day period immediately preceding the Effective Date.

          (v) Expenses.  During the Employment Period, the Executive shall be
              --------                                                       
entitled to receive prompt reimbursement for all reasonable expenses incurred by
the Executive in accordance with the most favorable policies, practices and
procedures of the Company and its affiliated companies in effect for the
Executive at any time during the 90-day period immediately preceding the
Effective Date or, if more favorable to the Executive, as in effect at any time
thereafter generally with respect to other peer executives of the Company and
its affiliated companies.

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          (vi) Fringe Benefits.  During the Employment Period, the Executive
               ---------------                                              
shall be entitled to fringe benefits in accordance with the most favorable
plans, practices, programs and policies of the Company and its affiliated
companies in effect for the Executive at any time during the 90-day period
immediately preceding the Effective Date or, if more favorable to the Executive,
as in effect at any time thereafter generally with respect to other peer
executives of the Company and its affiliated companies.

          (vii) Office and Support Staff.  During the Employment Period, the
                ------------------------                                    
Executive shall be entitled to an office or offices of a size and with
furnishings and other appointments, and to personal secretarial and other
assistance, at least equal to the most favorable of the foregoing provided to
the Executive by the Company and its affiliated companies at any time during the
90-day period immediately preceding the Effective Date or, if more favorable to
the Executive, as provided at any time thereafter generally with respect to
other peer executives of the Company and its affiliated companies.

          (viii) Vacation.  During the Employment Period, the Executive shall be
                 --------                                                       
entitled to paid vacation in accordance with the most favorable plans, policies,
programs and practices of the Company and its affiliated companies as in effect
for the Executive at any time during the 90-day period immediately preceding the
Effective Date or, if more favorable to the Executive, as in effect at any time
thereafter generally with respect to other peer executives of the Company and
its affiliated companies.

      5. Termination of Employment.
         ------------------------- 

      (a) Death or Disability.  The Executive's employment shall terminate
          -------------------                                             
automatically upon the Executive's death during the Employment Period.  If the
Company determines in good faith that the Disability (as defined below) of the
Executive has occurred during the Employment Period, it may give to the
Executive written notice in accordance with Section 12(b) of this Agreement of
its intention to terminate the Executive's employment.  In such event, the
Executive's employment with the Company shall terminate effective on the 30th
day after receipt of such notice by the Executive (the "Disability Effective
Date"), provided that, within the 30 days after such receipt, the Executive
shall not have returned to full-time performance of the Executive's duties.  For
purposes of this Agreement, "Disability" means the absence of the Executive from
the Executive's duties with the Company on a full-time basis for 180 consecutive
business days as a result of incapacity due to mental or physical illness which
is determined to be total and permanent by a physician selected by the Company
or its insurers and acceptable to the Executive or the Executive's legal
representative (such agreement as to acceptability not to be withheld
unreasonably).

      (b) Cause.  The Company may terminate the Executive's employment during
          -----                                                              
the Employment Period for "Cause".  For purposes of this Agreement, "Cause"
means (i) repeated violations by the Executive of the Executive's obligations
under Section 4(a) of this Agreement which are demonstrably willful and
deliberate on the Executive's part and which are not remedied in a reasonable
period of time after receipt of written notice from the Company, (ii) commission
of an intentional act of fraud, embezzlement or theft by the Executive in
connection with the Executive's duties or in the course of the 

                                      E-6
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Executive's employment with the Company, (iii) causing intentional wrongful
damage to property of the Company, (iv) intentionally and wrongfully disclosing
secret processes or confidential information of the Company, or (v)
participating, without the Company's consent, in the management of any business
enterprise which engages in substantial and direct competition with the Company,
and any such act shall have been materially harmful to the Company.

      (c) Good Reason.  The Executive's employment may be terminated during the
          -----------                                                          
Employment Period by the Executive for Good Reason.  For purposes of this
Agreement, "Good Reason" means

      (i) the assignment to the Executive of any duties inconsistent in any
respect with the Executive's position (including status, offices, titles and
reporting requirements), authority, duties or responsibilities as contemplated
by Section 4(a) of this Agreement, or any other action by the Company with
results in a diminution in such position, authority, duties or responsibilities,
excluding for this purpose an isolated, insubstantial and inadvertent action not
taken in bad faith and which is remedied by the Company promptly after receipt
or written notice thereof given by the Executive;

      (ii) any failure by the Company to comply with any of the provisions of
Section 4(b) of this Agreement, other than an isolated, insubstantial and
inadvertent failure not occurring in bad faith and which is remedied by the
Company promptly after receipt of written notice thereof given by the Executive;

      (iii) the Company requiring the Executive to be based at any office or
location other than that described in Section 4(a) (i) (B) hereof or, requiring
the Executive to travel away from Executive's office in the course of
discharging responsibilities or duties in a manner which is inappropriate for
the performance of the Executive's duties hereunder and which is significantly
more frequent (in terms of either consecutive days or aggregate days in any
calendar year) than was required prior to the Change of Control;

      (iv) any purported termination by the Company of the Executive's
employment otherwise than as expressly permitted by this Agreement; or

      (v) any failure by any successor to comply with and satisfy Section 11 (c)
of this Agreement, provided that such successor has received at least ten days
prior written notice from the Company or the Executive of the requirements of
Section 11(c) of this Agreement.

      For the purposes of this Section 5(c), any good faith determination of
"Good Reason" made by the Executive shall be conclusive.

      (d)  Notice of Termination.  Any termination by the Company for Cause or
           ---------------------                                              
by the Executive for good Reason shall be communicated by Notice of Termination
to the other party hereto given in accordance with Section 12(b) of this
Agreement.  For purposes of this Agreement, a "Notice of Termination" means a
written notice which (i) indicates the specific termination provision in this
Agreement relied upon, (ii) to the extent applicable, sets forth in reasonable
detail the facts and circumstances claimed to provide a basis for termination of
the Executive's employment under the provision so indicated and (iii) if the
Date of Termination (as defined below) is other than the date of 

                                      E-7
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receipt of such notice, specifies the termination date (which date shall be not
more than fifteen days after the giving of such notice). The failure by the
Executive or the Company to set forth in the Notice of Termination any fact or
circumstance which contributes to a showing of Good Reason or Cause, as the case
may be, shall not waive any right of the Executive or the Company hereunder or
preclude the Executive or the Company from asserting such fact or circumstance
in enforcing the Executive's or the Company's rights hereunder.

      (e)  Date of Termination.  "Date of Termination" means the date of receipt
           -------------------                                                  
of the Notice of Termination or any later date specified therein, as the case
may be; provided, however, that (i) if the Executive's employment is terminated
by the Company other than for Cause or Disability, the Date of Termination shall
be the date on which the Company notifies the Executive of such termination and
(ii) if the Executive's employment is terminated by reason of death or
Disability, the Date of Termination shall be the date of death of the Executive
or the Disability Effective Date, as the case may be.

      6.  Obligations of the Company upon Termination.
          ------------------------------------------- 

      (a)  Death.  If the Executive's employment is terminated by reason of the
           -----                                                               
Executive's death during the Employment Period, this Agreement shall terminate
without further obligations to the Executive's legal representatives under this
Agreement, other than the following obligations:  (i) payment of the Executive's
Annual Base Salary through the Date of Termination to the extent not theretofore
paid, (ii) payment of the product of (x) the Annual Bonus paid or payable but
for any deferral (and annualized for any fiscal year consisting of less than
twelve full months or for which the Executive has been employed for less than
twelve full months) to the Executive for the most recently completed fiscal year
during the Employment Period, and (y) a fraction, the numerator of which is the
number of days in the current fiscal year through the Date of Termination, and
the denominator of which is 365 and (iii) payment of any compensation previously
deferred by the Executive (together with any accrued interest thereon) and not
yet paid by the Company and any accrued vacation pay not yet paid by the Company
(the amounts described in clauses (i), (ii) and (iii) above are hereafter
referred to as "Accrued Obligations").  All Accrued Obligations shall be paid to
the Executive's estate or beneficiary, as applicable, at the option of the
Company, either (x) in a lump sum in cash within 30 days of the Date of
Termination or (y) in twelve equal consecutive monthly installments, with the
first installment to be paid within 30 days of the Date of Termination.
Anything in this Agreement to the contrary notwithstanding, the Executive's
family shall be entitled to receive benefits at least equal to the most
favorable benefits provided generally by the Company and any of its affiliated
companies to surviving families of peer executives of the Company and such
affiliated companies under such plans, programs, practices and policies relating
to family death benefits, if any, as in effect generally with respect to other
peer executives and their families at any time during the 90-day period
immediately preceding the Effective Date or, if more favorable to the Executive
and/or the Executive's family as in effect on the date of the Executive's death
generally with respect to other peer executives of the Company and its
affiliated companies and their families.

      (b)  Disability.  If the Executive's employment is terminated by reason of
           ----------                                                           
the Executive's Disability during the Employment Period, this Agreement shall
terminate without further obligations to the Executive, other 

                                      E-8
<PAGE>
 
than for Accrued Obligations. All Accrued Obligations shall be paid to the
Executive at the option of the Company, either (x) in a lump sum in cash within
30 days of the Date of Termination or (y) in twelve equal consecutive monthly
installments, with the first installment to be paid within 30 days of the Date
of Termination. Anything in this Agreement to the contrary notwithstanding, the
Executive shall be entitled after the Disability Effective Date to receive
disability and other benefits at least equal to the most favorable of those
provided by the Company and its affiliated companies to disabled executives
and/or their families in accordance with such plans, programs, practices and
policies relating to disability, if any, as in effect generally with respect to
other peer executives and their families at any time during the 90-day period
immediately preceding the Effective Date or, if more favorable to the Executive
ad/or the Executive's family, as in effect at any time thereafter through the
Date of Termination generally with respect to other peer executives of the
Company and its affiliated companies and their families.

      (c)  Cause.  If the Executive's employment shall be terminated for Cause
           -----                                                              
during the Employment Period, this Agreement shall terminate without further
obligations to the Executive other than the obligation to pay to the Executive
the Annual Base Salary through the Date of Termination plus the amount of any
compensation previously deferred by the Executive, in each case to the extent
theretofore unpaid.  If the Executive terminates employment during the
Employment Period, excluding a termination for Good Reason, this Agreement shall
terminate without further obligations to the Executive, other than for Accrued
Obligations.  In such case, all Accrued Obligations shall be paid to the
Executive at the option of the Company, either (x) in a lump sum in cash within
30 days of the Date of Termination, or (y) in twelve equal consecutive monthly
installments, with the first installment to be paid within 30 days of the Date
of Termination.

      (d)  Good Reason.  If, during the Employment Period, the Company shall
           -----------                                                      
terminate the Executive's employment other than for Cause or Disability, or if
the Executive shall terminate employment under this Agreement for Good Reason:

      (i)  the Company shall pay to the Executive the aggregate of the following
amounts, such amounts, to be payable at the option of the Company, either (x) in
a lump sum in cash within 30 days of the Date of Termination or (y) in twelve
equal consecutive monthly installments, with the first installment to be paid
within 30 days of the Date of Termination:

      A.  all Accrued Obligations; and

      B.  1 times the sum of the Executive's Annual Base Salary and the
          -                                                            
Executive's Annual Bonus paid or payable but for any deferral (and annualized
for any fiscal year consisting of less than twelve full months or for which the
executive has been employed for less than twelve full months) to the Executive
for the most recently completed fiscal year during the Employment Period; and

      C.  the Executive shall be entitled to receive a separate lump-sum
supplemental retirement benefit equal to the difference between (a) the
actuarial equivalent (utilizing for this purpose the actuarial assumptions
utilized with respect to the Life Technologies Inc. Retirement Plan (or any
successor plan thereto) (the "Retirement Plan") during the 90-day period

                                      E-9
<PAGE>
 
immediately preceding the Effective Date) of the benefit payable under the
Retirement Plan and any supplemental and/or excess retirement plan providing
benefits for the Executive (the "SERP") which the Executive would receive if the
Executive's employment continued at the compensation levels provided for in
Section 4(b) (i) and 4(b)(ii) of this Agreement for the remainder of the
Employment Period, assuming for this purpose that all accrued benefits are fully
vested and that benefit accrual formulas are no less advantageous to the
Executive than those in effect during the 90-day period immediately preceding
the Effective Date, and (b) the actuarial equivalent (utilizing for this purpose
the actuarial assumptions utilized with respect to the Retirement Plan during
the 90-day period immediately preceding the Effective Date) of the Executive's
actual benefit (paid or payable), if any, under the Retirement Plan and the
SERP; and

      (ii) for the remainder of the Employment Period, or such longer period as
any plan, program, practice or policy may provide, the Company shall continue
benefits to the Executive and, where applicable, the Executive's family at least
equal to those which would have been provided to them in accordance with the
plans, programs, practices and policies described in Section 4(b) (iv) of this
Agreement if the Executive's employment had not been terminated in accordance
with the most favorable plans, practices, programs or policies of the Company
and its affiliated companies generally applicable to other peer executives and
their families during the 90-day period immediately preceding the Effective Date
or, if more favorable to the Executive, as in effect at any time thereafter
generally with respect to other peer executives of the Company and its
affiliated companies and their families.  For purposes of determining
eligibility of the Executive for retiree benefits pursuant to such plans,
practices, programs and policies, the Executive shall be considered to have
remained employed until the end of the Employment Period and to have retired on
the last day of such period.

The amounts required to be paid under this Section 6(d) shall be reduced by any
other amount of severance (i.e., relating solely to salary or bonus continuation
or actual or deemed pension or insurance continuation) received by the Executive
upon such termination of employment under any severance plan, policy or
arrangement of the Company applicable to the Executive or a group of employees
of the Company, including the Executive, and applicable without regard to the
occurrence of a change of control of Dexter or the Company prior to such
termination of employment.  The amounts payable to the Executive pursuant to
this Agreement will not be subject to any requirement of mitigation, nor will
they be offset or otherwise reduced by reason of Executive's receipt of
compensation from any source other than the Company.

      7.  Non-exclusivity of Rights.  Nothing in this Agreement shall prevent or
          -------------------------                                             
limit the Executive's continuing or future participation in any benefit, bonus,
incentive or other plans, programs, policies or practices provided by the
Company or any of its affiliated companies and for which the Executive may
qualify, nor shall anything herein limit or otherwise affect such rights as the
Executive may have under any other agreements with the Company or any of its
affiliated companies.  Amounts which are vested benefits or which the Executive
is otherwise entitled to receive under any plan, policy, practice or program of
the Company or any of its affiliated companies at or subsequent to the Date of
Termination shall be payable in accordance with such plan, policy, practice or
program except as explicitly modified by this Agreement.

                                      E-10
<PAGE>
 
      8.  Full Settlement.  The Company's obligation to make the payments
          ---------------                                                
provided for in this Agreement and otherwise to perform its obligations
hereunder, except as provided in the last sentence of Section 6(d), shall not be
affected by any set-off, counterclaim, recoupment, defense or other claim, right
or action which the Company may have against the Executive or others.  In no
event shall the Executive be obligated to seek other employment or take any
other action by way of mitigation of the amounts payable to the Executive under
any of the provisions of this Agreement.  The Company agrees to pay, to the full
extent permitted by law, all legal fees and expenses which the Executive may
reasonably incur as a result of any contest (regardless of the outcome thereof)
by the Company or others of the validity or enforceability of, or liability
under, any provision of this Agreement or any guarantee of performance thereof
(including as a result of any contest by the Executive about the amount of any
payment pursuant to this Agreement), plus in each case interest on any delayed
payment at the applicable Federal rate provided for in Section 7872(f)(2) of the
Internal Revenue Code of 1986, as amended (the "Code").

      9.  Certain Additional Provisions.
          ----------------------------- 

      (a)  Anything in this Agreement to the Contrary notwithstanding, in the
event it shall be determined that, as a result, directly or indirectly, of the
operation of the Company's Stock Option Plan, or any successor option or
restricted Stock plans (the "Option and Restricted Stock Acceleration") or the
receipt of any other payment or distribution by the Company to or for the
benefit of the Executive whether paid or payable or distributed or distributable
pursuant to the terms of this Agreement or otherwise (a "Payment") the Executive
would be subject to the excise tax imposed by Section 4999 of the Code or any
interest or penalties are incurred by the Executive with respect to such excise
tax (such excise tax, together with any such interest and penalties, are
hereinafter collectively referred to as the "Excise Tax"), then the amount
payable to the Executive hereunder or as a result of the Option and Restricted
Stock Acceleration shall, at the election of Executive, be reduced in an amount
that would result in the Executive being in the most advantageous net after-tax
position (taking into account both income taxes and any Excise Tax).  For
purposes of this determination, the "base amount" as defined in Section N
280G(b) (3)(A) of the Code shall be allocated between the Option and Restricted
Stock Acceleration, on the one hand, and Payments, on the other hand, in
accordance with Section 280G(b)(3)(B) of the Code.

      (b)  All determinations required to be made under this Section 9,
including the amount of any reduction that will be made in the payments made
pursuant to this Agreement and the assumptions to be utilized in arriving at
such determinations, shall be made by Coopers & Lybrand (the "Accounting Firm")
which shall provide detailed supporting calculations both to the Company and the
Executive.  All fees and expenses of the Accounting Firm shall be borne solely
by the Company.  If the Accounting Firm determines that no Excise Tax is payable
by the Executive, it shall furnish the Executive with an opinion that failure to
report the Excise Tax on the Executive's applicable federal income tax return
would not result in the imposition of a negligence or similar penalty.  Any
determination by the Accounting Firm shall be binding upon the Company and the
Executive.

                                      E-11
<PAGE>
 
      10.  Confidential Information.  The Executive shall hold in a fiduciary
           ------------------------                                          
capacity for the benefit of the Company all secret or confidential information,
knowledge or data relating to the Company or any of its affiliated companies,
and their respective businesses, which shall have been obtained by the Executive
during the Executive's employment by the Company or any of its affiliated
companies and which shall not be or become public knowledge (other than by acts
by the Executive or representatives of the Executive's employment with the
Company, the Executive shall not, without the prior written consent of the
Company, communicated or divulge any such information, knowledge or date to
anyone other than the Company and those designated by it.  In addition, to the
extent that the Executive is a party to any other agreement relating to
confidential information, inventions or similar matters with the Company, the
Executive shall continue to comply with the provisions of such agreements.  In
no event shall an asserted violation of the provisions of this Section 10
constitute a basis for deferring or withholding any amounts otherwise payable to
the Executive under this Agreement.

      11.  Successors.  (a)  This Agreement is personal to the Executive and
           ----------                                                       
without the prior written consent of the Company shall not be assignable by the
Executive otherwise than by will or the laws of descent and distribution.  This
Agreement shall inure to the benefit of and be enforceable by the Executive's
legal representatives.

      (b)  This Agreement shall inure to the benefit of and be binding upon the
Company and its successors and assigns.

      (c)  The Company will require any successor (whether direct or indirect,
by purchase, merger, consolidation or otherwise) to all or substantially all of
the business and/or assets of the Company to assume expressly and agree to
perform this Agreement in the same manner and to the same extent that the
Company would be required to perform it if no such succession had taken place.
As used in this Agreement, "Company" shall mean the Company as hereinbefore
defined and any successor to its business and/or assets as aforesaid which
assumes and agrees to perform this Agreement by operation of law, or otherwise.

      12.  Miscellaneous.  (a)  This Agreement shall be governed by and
           -------------                                               
construed in accordance with the laws of the State of New York, without
reference to principles of conflict of laws.

The captions of this Agreement are not part of the provisions hereof and shall
have no force or effect.  This Agreement may not be amended or modified
otherwise than by a written agreement executed by the parties hereto or their
respective successors and legal representatives.

      (b)  All notices and other communications hereunder shall be in writing
and shall be given by hand delivery to the other party or by registered or
certified mail, return receipt requested, postage prepaid, addressed as follows:

                                      E-12
<PAGE>
 
      If to the Executive:
      ------------------- 
      John E. Leffler
      c/o Life Technologies, Inc.
      8717 Grovemont Circle
      Gaithersburg, MD  20877

      If to the Company:
      ----------------- 
      Life Technologies, Inc.
      8717 Grovemont Circle
      Gaithersburg, MD  20877
      Attn:  President

or to such other address as either party shall have furnished to the other in
writing in accordance herewith.  Notice and communications shall be effective
when actually received by the addressee.

      (c)  The invalidity or unenforceability of any provision of this Agreement
shall not affect the validity or enforceability of any other provision of this
Agreement.

      (d)  The Company may withhold from any amounts payable under this
Agreement such Federal, state or local taxes as shall be required to be withheld
pursuant to any applicable law or regulation.

      (e)  The Executive's or the Company's failure to insist upon strict
compliance with any provision hereof in any particular instance shall not be
deemed to be a waiver of such provision or any other provision thereof.

      IN WITNESS WHEREOF, the Executive has hereunto set his hand and, pursuant
to the authorization from its Board of Directors, the Company has caused these
presents to be executed in its name on its behalf, all as of the day and year
first above written.


                                      /s/ John E. Leffler
                                      -------------------
                                      [Executive]

                                      LIFE TECHNOLOGIES, INC.

                                      By:/s/ J. Stark Thompson
                                         ---------------------
                                         President and CEO

                                      E-13