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):

                                December 10, 1998

                   ----------------------------------------


                                 THERMEDICS INC.
             (Exact name of Registrant as specified in its charter)


Massachusetts                   1-9567                    04-2788806
(State or other               (Commission               (I.R.S. Employer
jurisdiction of               File Number)             Identification Number) 
incorporation or
organization)


470 Wildwood Street, P.O. Box 2999
Woburn, Massachusetts                                  01888
(Address of principal executive offices)            (Zip Code)


                                (781) 938-3786
                         (Registrant's telephone number
                              including area code)









      This Form 8-K contains forward-looking statements that involve a number of
risks and  uncertainties.  Important  factors that could cause actual results to
differ  materially from those indicated by such  forward-looking  statements are
set forth under the heading  "Forward-looking  Statements"  in Exhibit 13 to the
Registrant's  Annual  Report on Form 10-K for the year  ended  January  3, 1998.
These include risks and  uncertainties  relating to:  government  regulation and
industry standards,  competition and technological change, intellectual property
rights,  reimbursement  by insurers for medical  procedures,  medical  community
acceptance of medical devices, availability of materials and components, product
liability,  international  operations,  the Registrant's spinout and acquisition
strategies,   and  the   potential   impact  of  the  year  2000  on  processing
date-sensitive information.

Item 5.     Other Events

      On December 10, 1998, Thermo Electron Corporation ("Thermo Electron"), the
Registrant's parent  corporation,  issued a press release regarding an update to
the proposed corporate  reorganization,  announced on August 12, 1998, involving
certain of Thermo Electron's subsidiaries, including the Registrant.

      The press release  stated,  among other things,  that Thermo  Sentron Inc.
("Thermo  Sentron"),  a  majority-owned,   publicly  traded  subsidiary  of  the
Registrant,  will not be combined  with  Metrika  Systems  Corporation  and ONIX
Systems  Inc.,  both  majority-owned,  publicly  traded  subsidiaries  of Thermo
Instrument Systems Inc. ("Thermo Instrument"),  to form a new sensor and process
control  company,  as had been  announced on August 12. In  addition,  the press
release stated that the Registrant will transfer its shares of its  subsidiaries
Thermo Sentron,  Thermedics Detection Inc.  ("Thermedics  Detection") and Thermo
Voltek Corp. ("Thermo Voltek"), along with additional shares of the Registrant's
Common Stock, to Thermo Electron in exchange for Thermo  Electron's wholly owned
biomedical  group.  The  Registrant's  shares  in  Thermo  Sentron,   Thermedics
Detection and Thermo Voltek will not be transferred to Thermo Instrument, as had
been announced on August 12.

      The completion of these  transactions  is subject to numerous  conditions,
including  the  establishment  of prices and exchange  ratios;  confirmation  of
anticipated  tax  consequences;  the  approval by the board of  directors of the
Registrant (including its independent  directors);  negotiation and execution of
definitive  agreements;  clearance by the Securities and Exchange  Commission of
any necessary documents in connection with the proposed  transactions;  approval
by the board of directors of Thermo Electron;  and receipt of fairness  opinions
from one or more investment  banking firms on certain  financial  aspects of the
transactions.


Item 7.     Financial Statements, Pro Forma Financial Information and Exhibits

      (a)    Financial Statements of Business Acquired: not
            applicable.

      (b)   Pro Forma Financial Information: not applicable.

      (c)   Exhibits: not applicable.









                                    SIGNATURE


      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 10th day of December, 1998.



                                          THERMEDICS INC.



                                    By: /s/  Kenneth J. Apicerno
                                             Kenneth J. Apicerno
                                             Treasurer