Exhibit 10.20
                         THERMO BIOANALYSIS CORPORATION

                     RESTATED STOCK HOLDING ASSISTANCE PLAN


        SECTION 1.   Purpose.

             The purpose of this Plan is to benefit Thermo BioAnalysis
        Corporation (the "Company") and its stockholders by encouraging
        Key Employees to acquire and maintain share ownership in the
        Company, by increasing such employees' proprietary interest in
        promoting the growth and performance of the Company and its
        subsidiaries and by providing for the implementation of the Stock
        Holding Policy.  

        SECTION 2.     Definitions.

             The following terms, when used in the Plan, shall have the
        meanings set forth below:

             Committee:   The Human Resources Committee of the Board of
        Directors of the Company as appointed from time to time.

             Common Stock:   The common stock of the Company and any
        successor thereto.

             Company:   Thermo BioAnalysis Corporation, a Delaware
        corporation.

             Stock Holding Policy:   The Stock Holding Policy of the
        Company, as adopted by the Committee and as in effect from time
        to time.

             Key Employee:   Any employee of the Company or any of its
        subsidiaries, including any officer or member of the Board of
        Directors who is also an employee, as designated by the
        Committee, and who, in the judgment of the Committee, will be in
        a position to contribute significantly to the attainment of the
        Company's strategic goals and long-term growth and prosperity.

             Loans:   Loans extended to Key Employees by the Company
        pursuant to this Plan.

             Plan:   The Thermo BioAnalysis Corporation Stock Holding
        Assistance Plan, as amended from time to time.

        SECTION 3.     Administration.

             The Plan and the Stock Holding Policy shall be administered
        by the Committee, which shall have authority to interpret the
        Plan and the Stock Holding Policy and, subject to their
        provisions, to prescribe, amend and rescind any rules and
        regulations and to make all other determinations necessary or
        desirable for the administration thereof.  The Committee's
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        interpretations and decisions with regard to the Plan and the
        Stock Holding Policy and such rules and regulations as may be
        established thereunder shall be final and conclusive.  The
        Committee may correct any defect or supply any omission or
        reconcile any inconsistency in the Plan or the Stock Holding
        Policy, or in any Loan in the manner and to the extent the
        Committee deems desirable to carry it into effect.  No member of
        the Committee shall be liable for any action or omission in
        connection with the Plan or the Stock Holding Policy that is made
        in good faith.

        SECTION 4.     Loans and Loan Limits.

             The Committee has determined that the provision of Loans
        from time to time to Key Employees in such amounts as to cause
        such Key Employees to comply with the Stock Holding Policy is, in
        the judgment of the Committee, reasonably expected to benefit the
        Company and authorizes the Company to extend Loans from time to
        time to Key Employees in such amounts as may be requested by such
        Key Employees in order to comply with the Stock Holding Policy.
        Such Loans may be used solely for the purpose of acquiring Common
        Stock (other than upon the exercise of stock options or under
        employee stock purchase plans) in open market transactions or
        from the Company.

             Each Loan shall be full recourse and evidenced by a
        non-interest bearing promissory note substantially in the form
        attached hereto as Exhibit A (the "Note") and maturing in
        accordance with the provisions of Section 6 hereof, and
        containing such other terms and conditions, which are not
        inconsistent with the provisions of the Plan and the Stock
        Holding Policy, as the Committee shall determine in its sole and
        absolute discretion.

        SECTION 5.     Federal Income Tax Treatment of Loans.

             For federal income tax purposes, interest on Loans shall be
        imputed on any interest free Loan extended under the Plan.  A Key
        Employee shall be deemed to have paid the imputed interest to the
        Company and the Company shall be deemed to have paid said imputed
        interest back to the Key Employee as additional compensation.
        The deemed interest payment shall be taxable to the Company as
        income, and may be deductible to the Key Employee to the extent
        allowable under the rules relating to investment interest.  The
        deemed compensation payment to the Key Employee shall be taxable
        to the employee and deductible to the Company, but shall also be
        subject to employment taxes such as FICA and FUTA.

        SECTION 6.     Maturity of Loans.

             Each Loan to a Key Employee hereunder shall be due and
        payable on demand by the Company.  If no such demand is made,
        then each Loan shall mature and the principal thereof shall
        become due and payable in five equal annual installments from the

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        payment of annual cash incentive compensation (referred to as
        bonus) to the Key Employee by the Company, beginning with the
        first such bonus payment to occur after the date of the Note
        evidencing the Loan, and on each of the next four bonus payment
        dates, provided that the Committee may, in its sole and absolute
        discretion, authorize such other maturity and repayment schedule
        as the Committee may determine.  Each Loan shall also become
        immediately due and payable in full, without demand, upon  the
        occurrence of any of the events set forth in the Note; provided
        that the Committee may, in its sole and absolute discretion,
        authorize an extension of the time for repayment of a Loan upon
        such terms and conditions as the Committee may determine.

        SECTION 7.     Amendment and Termination of the Plan.

             The Committee may from time to time alter or amend the Plan
        or the Stock Holding Policy in any respect, or terminate the Plan
        or the Stock Holding Policy at any time.  No such amendment or
        termination, however, shall alter or otherwise affect the terms
        and conditions of any Loan then outstanding to Key Employee
        without such Key Employee's written consent, except as otherwise
        provided herein or in the promissory note evidencing such Loan.

        SECTION 8.     Miscellaneous Provisions.

             (a)  No employee or other person shall have any claim or
        right to receive a Loan under the Plan, and no employee shall
        have any right to be retained in the employ of the Company due to
        his or her participation in the Plan.

             (b)  No Loan shall be made hereunder unless counsel for the
        Company shall be satisfied that such Loan will be in compliance
        with applicable federal, state and local laws.

             (c)  The expenses of the Plan shall be borne by the Company.

             (d)  The Plan shall be unfunded, and the Company shall not
        be required to establish any special or separate fund or to make
        any other segregation of assets to assure the making of any Loan
        under the Plan.

             (e)  Except as otherwise provided in Section 7 hereof, by
        accepting any Loan under the Plan, each Key Employee shall be
        conclusively deemed to have indicated his acceptance and
        ratification of, and consent to, any action taken under the Plan
        or the Stock Holding Policy by the Company, the Board of
        Directors of the Company or the Committee.

             (f)  The appropriate officers of the Company shall cause to
        be filed any reports, returns or other information regarding
        Loans hereunder, as may be required by any applicable statute,
        rule or regulation.

        SECTION 9.     Effective Date.

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             The Plan and the Stock Holding Policy shall become effective
        upon approval and adoption by the Committee.















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                               EXHIBIT A TO STOCK HOLDING ASSISTANCE PLAN


                         THERMO BIOANALYSIS CORPORATION

                                 Promissory Note



        $_________                                                       
                                                Dated:____________


             For value received, ________________, an individual whose
        residence is located at _______________________ (the "Employee"),
        hereby promises to pay to Thermo BioAnalysis Corporation (the
        "Company"), or assigns, ON DEMAND, but in any case on or before
        [insert date which is the fifth anniversary of date of issuance]
        (the "Maturity Date"), the principal sum of [loan amount in
        words] ($_______), or such part thereof as then remains unpaid,
        without interest.  Principal shall be payable in lawful money of
        the United States of America, in immediately available funds, at
        the principal office of the Company or at such other place as the
        Company may designate from time to time in writing to the
        Employee. 

              Unless the Company has already made a demand for payment in
        full of this Note, the Employee agrees to repay the Company  an
        amount equal to 20% of the initial principal amount of the Note
        from the payment of annual cash incentive compensation (referred
        to as bonus) to the Employee by the Company, beginning with the
        first such bonus payment to occur after the date of this Note,
        and on each of the next four bonus payment dates.  Any amount
        remaining unpaid under this Note, if no demand has been made by
        the Company, shall be due and payable on the Maturity Date.

             This Note may be prepaid at any time or from time to time,
        in whole or in part, without any premium or penalty.  The
        Employee acknowledges and agrees that the Company has advanced to
        the Employee the principal amount of this Note pursuant to the
        Company's Stock Holding Assistance Plan, and that all terms and
        conditions of such Plan are incorporated herein by reference.  

             The unpaid principal amount of this Note shall be and become
        immediately due and payable without notice or demand, at the
        option of the Company, upon the occurrence of any of the
        following events:

                  (a)  the termination of the Employee's employment with
        the Company, with or without cause, for any reason or for no
        reason;

                  (b)  the death or disability of the Employee;

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                  (c)  the failure of the Employee to pay his or her
        debts as they become due, the insolvency of the Employee, the
        filing by or against the Employee of any petition under the
        United States Bankruptcy Code (or the filing of any similar
        petition under the insolvency law of any jurisdiction), or the
        making by the Employee of an assignment or trust mortgage for the
        benefit of creditors or the appointment of a receiver, custodian
        or similar agent with respect to, or the taking by any such
        person of possession of, any property of the Employee; or

                  (d)  the issuance of any writ of attachment, by trustee
        process or otherwise, or any restraining order or injunction not
        removed, repealed or dismissed within thirty (30) days of
        issuance, against or affecting the person or property of the
        Employee or any liability or obligation of the Employee to the
        Company.

             In case any payment herein provided for shall not be paid
        when due, the Employee further promises to pay all costs of
        collection, including all reasonable attorneys' fees.

             No delay or omission on the part of the Company in
        exercising any right hereunder shall operate as a waiver of such
        right or of any other right of the Company, nor shall any delay,
        omission or waiver on any one occasion be deemed a bar to or
        waiver of the same or any other right on any future occasion.
        The Employee hereby waives presentment, demand, notice of
        prepayment, protest and all other demands and notices in
        connection with the delivery, acceptance, performance, default or
        enforcement of this Note.  The undersigned hereby assents to any
        indulgence and any extension of time for payment of any
        indebtedness evidenced hereby granted or permitted by the
        Company.  

             This Note has been made pursuant to the Company's Stock
        Holding Assistance Plan and shall be governed by and construed in
        accordance with, such Plan and the laws of the State of Delaware
        and shall have the effect of a sealed instrument.


                                      _______________________________

                                      Employee Name: _________________


        ________________________
        Witness