SECURITIES AND EXCHANGE COMMISSION

                             Washington, D.C. 20549

                     _______________________________________

                                    FORM 8-K

                                 CURRENT REPORT

                       Pursuant to Section 13 or 15(d) of
                       the Securities Exchange Act of 1934

                                 Date of Report
                       (Date of earliest event reported):

                                 March 26, 1997

                     _______________________________________

                         THERMO INSTRUMENT SYSTEMS INC.
             (Exact name of Registrant as specified in its charter)

        Delaware                  1-9786             04-2925809
        (State or other           (Commission        (I.R.S. Employer
        jurisdiction of            File Number)   Identification Number)
        incorporation)

        1275 Hammerwood Avenue
        Sunnyvale, CA                                     94089
        (Address of principal                             (Zip Code)
         executive offices)
                                 (617) 622-1000
                         (Registrant's telephone number
                              including area code)
PAGE



                                        2



        Item 2.   Acquisition or Disposition of Assets
                  ------------------------------------

             On March 26, 1997, Thermo Instrument Systems Inc. (the
        "Company") acquired 164,126,284 shares of Life Sciences
        International PLC ("Life Sciences"), a London Stock Exchange
        listed company, for 135 pence per share (an aggregate of
        approximately $355,000,000) in completion of the Company's offer
        to acquire all of the outstanding shares of Life Sciences. The
        Company became unconditionally obligated to acquire these shares
        on March 12, 1997 after the Company declared the offer
        unconditional in all respects.  The Company will acquire the Life
        Sciences shares that remain outstanding (approximately 10,600,000
        shares) for 135 pence per share pursuant to the compulsory
        acquisition rules applicable to United Kingdom companies. The
        acquisition of the Life Sciences shares was financed with
        available cash and borrowings from Thermo Electron Corporation
        ("Thermo Electron"), the Company's parent corporation.

             The Company has no present intention to use the plant,
        equipment or other physical property acquired for purposes
        materially different for the purposes for which such assets were
        used prior to the acquisition.   The Company will review the  
        businesses of Life Sciences and their assets, corporate
        structure, capitalization, operations, properties, policies,
        management and personnel.  The Company may develop plans or
        proposals, including mergers, transfers of a material amount of
        assets or other transactions or changes relating to the acquired
        businesses.  Any such transaction might involve Thermo Electron
        or another subsidiary of Thermo Electron or the Company.



        Item 7.   Financial Statements, Pro Forma Combined Condensed
                  --------------------------------------------------
                  Financial Information and Exhibits.
                  ----------------------------------


                  (a)  Financial Statements of Businesses Acquired:  As
                       it is impracticable to file such information at
                       this time, it will be filed by amendment on or
                       prior to June 9, 1997.

                  (b)  Pro Forma Combined Condensed Financial
                       Information:  as it is impracticable to file such
                       information at this time, it will be filed by
                       amendment on or prior to June 9, 1997.
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                                   SIGNATURES


             Pursuant to the requirements of the Securities Exchange Act
        of 1934, the Registrant has duly caused this report to be signed
        on its behalf by the undersigned thereunto duly authorized, on
        this 3d day of April, 1997.

                                      THERMO INSTRUMENT SYSTEMS INC.



                                      By: /s/Jonathan W. Painter
                                           Jonathan W. Painter
                                           Treasurer





        AA970870010