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                                                                    Exhibit 10.4

                          CHANGE-IN-CONTROL AGREEMENT


          AGREEMENT by and between LIFE TECHNOLOGIES, INC., a Delaware
Corporation (the "Company"), and John E. Leffler  (the "Executive"), dated as of
the 13th day of February 1997.

          The Board of Directors of the Company (the "Board"), has determined
that it is in the best interests of the Company and its stockholders 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 l(b)) on which a Change of Control
occurs; provided that the Executive is employed on that date.  Anything in this
Agreement to the contrary notwithstanding, if the Executive's employment with
the Company is terminated or the Executive ceases to be an officer of the
Company prior to the date on which a Change of Control occurs, and it is
reasonably demonstrated by the Executive that such termination of employment or
cessation of status as an officer (i) was at the request of a third party who
has taken steps reasonably calculated to effect the Change of Control or (ii)
otherwise arose in connection with or anticipation of the Change of Control,
then for all purposes of this Agreement the "Effective Date" shall mean the date
immediately prior to the date of such termination of employment or cessation of
status as an officer.

          (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.

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

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

          (i) Any acquisition or series of acquisitions, 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 20% 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 (A) any acquisition by the Company, The
Dexter Corporation ("Dexter") or any of their subsidiaries, (B) any acquisition
by any employee benefit plan (or related trust) sponsored or maintained by the
Company, Dexter or any of their subsidiaries, (C) any transaction or series of
transactions that results in any individual, entity or group (within the meaning
of Section 13(d)(3) or 14(d)(2) of the Exchange Act) having beneficial ownership
(within the meaning of Rule 13d-3 under the Exchange Act) of more than 20% of
the Outstanding Company Common Stock but less than the percentage of Outstanding
Company Common Stock then beneficially owned by Dexter, or (D) any acquisition
or series of acquisitions which results in any individual, entity or group
(within the meaning of Section 13(d)(3) or 14(d)(2) of the Exchange Act)
acquiring beneficial ownership (within the meaning of Rule 13d-3 under the
Exchange Act) of more than 20% of the Outstanding Company Common Stock and while
such a beneficial owner such individual, entity or group does not exercise the
voting power of his, her or its Outstanding Company Common Stock or otherwise
exercise control with respect to any matter concerning or affecting the Company
and promptly sells, transfers, assigns or otherwise disposes of that number of
shares of Outstanding Company Common Stock necessary to reduce his, her or its
beneficial ownership (within the meaning of Rule 13d-3 under the Exchange Act)
of the Outstanding Company Common Stock to below 20%, as the case may be, shall
not constitute a Change of Control; or

          (ii) Individuals who as of December 1, 1996, 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 December 1, 1996,
whose election, or nomination for election, by the Company's stockholders 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 (as hereinafter defined), 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 used
in Rule 14a-11 of the Regulation 14A promulgated under the Exchange Act)
relating to the election of directors of the Company; or


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                    (iii)  Approval by the stockholders of the Company of a
          complete liquidation or dissolution of the Company, or of the sale or
          other disposition of all or substantially all of the assets of the
          Company, or of a reorganization, merger or consolidation of the
          Company, 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 Company Common Stock and Outstanding Company
          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 60%
          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; or

                    (iv) At any time when 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 any of the events set forth in the following clauses
          (A), (B) or (C) below shall occur:

               (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 (I) any acquisition by the Company, Dexter or any of
          their subsidiaries, (II) any acquisition by any employee benefit plan
          (or related trust) sponsored or maintained by the Company, Dexter or
          any of their subsidiaries, or (III) any acquisition by any corporation
          with respect to which, following such acquisition, more than 60% of,
          respectively, the then outstanding shares 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 of 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

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               (B) Individuals who, as of December 1, 1996, 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
          December 1, 1996, whose election, or nomination for election, by
          Dexter's stockholders 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 of Dexter, 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 60% 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 stockholder of Dexter or any of its
subsidiaries (other than the Company and its subsidiaries) or an officer,
director, partner, employee or 5% or greater stockholder 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 remuneration 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 24th 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 50 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 and, 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 the highest 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)
base salary paid or payable to the Executive by the Company and its affiliated
companies in respect of the three fiscal years immediately preceding the fiscal
year 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, an annual
bonus (the "Annual Bonus") in cash at least equal to the higher of 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

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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 and/or the
Executive's family at any time during the 90-day period immediately preceding
the Effective Date.

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          (v) Business Expenses.  During the Employment Period, the Executive
              -----------------                                              
shall be entitled to receive prompt reimbursement for all reasonable business
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.

          (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 15(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
responsibilities and duties 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 


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

          (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 responsibilities or 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 which 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 of 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 his or her 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 the Company to comply with and
satisfy Section 14(c) of this Agreement, provided that such successor has
received at least ten (10) days prior written notice from the Company or the
Executive of the requirements of Section 14(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 15(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 

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of Termination (as defined below) is other than the date of 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 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.


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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 peer 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 and/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 the
Executive shall terminate employment under this Agreement for Good Reason:


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          (i) the Company shall pay to the Executive the aggregate of the
following amounts, such amounts to be payable by the Company in a lump sum in
cash within 30 days of the Date of termination.

          A.   All Accrued Obligations; and

          B.   1.5 times the sum of the Executive's Annual Base Salary and the
               ---                                             
higher of either (i) 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 (ii) the targeted annual bonus payable to the
Executive pursuant to the Company's Incentive Compensation Plan for the fiscal
year in which the Date of Termination occurs (assuming 100% achievement of the
Company performance factor and 100% achievement of the Executive's personal
performance factor; 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
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 level 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

          D. An amount equal to that portion, if any, of the Company's 
contribution to the Executive's 401(k), savings or other similar individual
account plan which is not vested as of the Date of Termination (the "Unvested
Company Contribution"), plus an amount which when added to the Unvested Company
Contribution would be sufficient after Federal, state and local income taxes
(based on the tax returns filed by the Executive most recently prior to the Date
of Termination) to enable the Executive to net an amount equal to the Unvested
Company Contribution; and

          (ii) the Company shall pay the Executive up to $25,000 for executive
outplacement services utilized by the Executive upon the receipt by the Company
of written receipts or other appropriate documentation; and


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<PAGE>
 
          (iii)  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; provided, however, that if the
Executive becomes employed elsewhere during the Employment Period and is thereby
afforded comparable insurance and welfare benefits to those described in Section
4(b)(iv), the Company's obligation to continue providing the Executive with such
benefits shall cease or be correspondingly reduced, as the case may be.  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; and

          (iv) All outstanding stock options held by the Executive pursuant to
any Company stock option plan shall immediately become vested and exercisable as
to all or any part of the shares covered thereby, with the Executive being able
to exercise his or her stock options within a period of three months following
the Date of Termination or such longer period as may be permitted under
Executive's stock option agreements; and

          (v) If, in the calendar year immediately preceding the Date of
Termination, the Executive had relocated the Executive's primary residence from
one location (the "Point of Origin") to its location at the Date of Termination
at the request of the Company, then any relocation expenses that are actually
incurred in the year immediately following the Date of Termination by the
Executive in moving the Executive's primary residence to any location shall be
reimbursed by the Company to the extent such expenses do not exceed the cost of
relocating the Executive's primary residence to the Point of Origin, provided
such expenses are substantiated by means of written receipts.  The cost of
relocating the Executive's primary residence to the Point of Origin shall be
determined by averaging estimates obtained by the Company in writing from three
reputable moving companies, selected by the Company in good faith.  It shall be
the obligation of the Executive to notify the Company in advance of any such
relocation so that such estimates may be obtained.

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 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, except as specifically set forth herein,
will they be offset or otherwise reduced by reason of the Executive's receipt of
compensation from any source other than the Company.

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<PAGE>
 
          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.

          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, including the costs and expenses of any arbitration
proceeding, 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 content 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"); provided that the
                                                        --------         
Executive's claim is not determined by a court of competent jurisdiction or an
arbitrator to be frivolous or otherwise entirely without merit.

          9.  Release.  Upon fulfillment of the Company's obligation to  make
              -------                                                        
the payments provided for in this Agreement and otherwise to perform its
obligations hereunder, the Executive fully and unconditionally releases and
discharges all claims and causes of action which the Executive or his or her
heirs, personal representatives, successors, or assigns ever had, now have, or
hereafter may have against the Company and any of its affiliated companies on
account of any claims and causes of action arising out of or relating to this
Agreement, any other document relating hereto or delivered in connection with
the transactions contemplated hereby.

          10.  Certain Additional Payments by the Company.
               ------------------------------------------ 

          (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 any of the Company's existing stock option plans, or any successor
option or restricted stock plans (collectively, the "Option and Restricted Stock
Acceleration"), either standing alone or taken together with 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 be reduced in an amount that would result in the Executive
being in the most 

                                      70
<PAGE>
 
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 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,
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 L.L.P. (the "Accounting
Firm") which shall provide detailed supporting calculations both to the Company
and the Executive.  All fees and expenses of the Accounting Firm for tax and
accounting advice provided to the Executive, up to a maximum of $15,000, 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.

          11.  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 in violation
of this Agreement).  After termination of the Executive's employment with the
Company, the Executive shall not, without the prior written consent of the
Company, communicate or divulge any such information, knowledge or data 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 constitute a
basis for deferring or withholding any amounts otherwise payable to the
Executive under this Agreement.

          12.  Public Announcements.  The Executive shall consult with the
               --------------------                                       
Company before issuing any press release or otherwise making any public
statement with respect to the Company or any of its affiliated companies, this
Agreement or the  transactions contemplated hereby, and the Executive shall not
issue any such press release or make any such public statement without the prior
written approval of the Company, except as may be required by applicable law,
rule or regulation or any self regulatory agency requirements, in which event
the Company shall have the right to review and comment upon any such press
release or public statement prior to its issuance.

          13.  Arbitration.  Any dispute, controversy or claim arising out of or
               -----------                                                      
relating to this Agreement, or any breach thereof, shall be determined and
settled by arbitration to be held in the City of New York pursuant to the labor
rules of the American Arbitration Association or any successor organization.
Any award rendered thereunder shall be final, conclusive and binding on the
parties.  Subject to the provisions of Section 8 hereof, each party shall pay
one-half of all costs and expenses of any arbitration proceeding brought
pursuant to this Section, and each party shall pay its own attorneys' fees and
expenses.

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<PAGE>
 
          14.  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.

          15.  Miscellaneous.
               ------------- 

          (a) This Agreement shall be governed by and construed in accordance
with the laws of the Sate 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:

                    If to the Executive:
                    ------------------- 
                    John E. Leffler
                    17417 Avenleigh Drive
                    Ashton
                    Maryland 20861

                    If to the Company:
                    ----------------- 
                    Life Technologies, Inc.
                    Post Office Box 6482
                    9800 Medical Center Drive
                    Rockville, MD  20850
                    (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.

                                      72
<PAGE>
 
          (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.

          (f) This Agreement shall replace and supersede the Executive's
Employment Agreement dated as of the 11th day of April 1995 between the
Executive and the Company and, upon execution hereof by the parties hereto, such
prior employment agreement shall become null and void.

     IN WITNESS WHEREOF, the Executive has hereunto set his or her 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
 

                                    LIFE TECHNOLOGIES, INC.


/s/ John E. Leffler                 By:  /s/ Joseph C. Stokes, Jr.
------------------                      -----------------------------
                                        Sr. Vice President and
                                        Chief Financial Officer


                                      73