content: 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):
  
                                  January 31, 2000
                               ----------------------
  
  
                              THERMEDICS DETECTION INC.
                            ----------------------------
               (Exact name of Registrant as specified in its charter)
  
  
  Massachusetts                      1-12745                            04-3106698
  --------------------------------------------------------------------------------
  (State or other                  (Commission                    (I.R.S. Employer
  jurisdiction of                  File Number)             Identification Number)
  incorporation or
  organization)
  
  
  220 Mill Road
  Chelmsford, Massachusetts                                             01824-4178
  --------------------------------------------------------------------------------
  (Address of principal executive offices)                              (Zip Code)
  
  
                                   (781) 622-1000
                           (Registrant's telephone number
                                including area code)
  
  
  
  <PAGE>
  
  
  
  
  
  
  
  
           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" included in Exhibit 13
  to Thermedics Detection Inc.'s Annual Report on Form 10-K for the year ended
  January 2, 1999. These include risks and uncertainties relating to: the market's
  acceptance of new products, the Registrant's ongoing product development efforts
  required by rapid technological change, the dependence of the
  security-instrument market on government regulation and the airline industry,
  the significance of certain customers to the Registrant, as well as risks
  associated with competition, potential product liability, international
  operations, proprietary technology rights, the Registrant's acquisition
  strategy, potential fluctuations in quarterly performance, and the potential
  impact of the year 2000 on processing date-sensitive information.
  
  Item 5.  Other Events
           ------------
  
           On January 31, 2000, the Registrant issued a press release, attached
  hereto as Exhibit 99, regarding certain corporate transactions affecting the
  Registrant.
  
  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
  
                    99 Press Release dated January 31, 2000.
  
  
  
  
  <PAGE>
  
  
  
  
                                      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 31st day of January, 2000.
  
  
                                                   THERMEDICS DETECTION INC.
  
  
                                                   By:/s/ Theo Melas-Kyriazi
                                                      ---------------------------
                                                          Theo Melas-Kyriazi
                                                          Chief Financial Officer
  
  
  
  
  <PAGE>
  
  
                                                                        Exhibit 99
  Investor Contact: 781-622-1111
  Media Contact: 781-622-1252
  
                         THERMEDICS DETECTION ANNOUNCES CASH
                             TENDER OFFER BY THERMEDICS
  
  CHELMSFORD, Mass., January 31, 2000 - Thermedics Detection Inc. (ASE-TDX), a
  Thermo Electron company (NYSE-TMO), announced today that its parent company,
  Thermedics Inc. (ASE-TMD), will make a cash tender offer for any and all of the
  outstanding shares of Thermedics Detection common stock at $8.00 per share. This
  action is part of a major reorganization plan under which Thermo Electron will
  spin in, spin off, and sell various businesses to focus solely on its core
  measurement and detection instruments business.
  
           Thermedics currently owns approximately 83.6 percent of the outstanding
  shares of Thermedics Detection common stock. Thermedics will condition the
  tender offer on receiving acceptances from holders of enough shares so that,
  when combined with its current share ownership, Thermedics' ownership reaches at
  least 90 percent. If Thermedics achieves this 90-percent-ownership threshold, it
  will acquire all remaining outstanding shares of Thermedics Detection common
  stock through a "short-form" merger in Massachusetts. Shareholders who do not
  tender shares to Thermedics during the tender offer would also receive $8.00 per
  share in cash for their stock in the short-form merger.
  
           Thermo Electron, which owns approximately 5.3 percent of the
  outstanding shares of Thermedics Detection common stock, will tender its shares
  to Thermedics in the tender offer.
  
           The tender offer and proposed subsequent short-form merger require
  Securities and Exchange Commission clearance of necessary filings; a short-form
  merger would not require Thermedics Detection board or shareholder approval.
  
           The Thermedics board of directors has approved pursuing this proposed
  tender offer and short-form merger in lieu of continuing negotiations over a
  merger price with the Thermedics Detection special committee of its board of
  directors.
  
           Thermedics plans to conduct the tender offer during the second quarter
  of 2000. If Thermedics successfully obtains ownership of at least 90 percent of
  the outstanding Thermedics Detection shares, it expects to complete the spin-in
  by the end of the second quarter of 2000.
  
           Thermedics Detection develops, manufactures, and markets high-speed
  systems used for product quality assurance in a variety of industrial and
  laboratory processes, as well as for security at airports, border crossings, and
  other checkpoints. More information is available on the Internet at
  http://www.thermo.com/subsid/tdx1.html.
  
  OTHER IMPORTANT INFORMATION:
  THE TENDER OFFER THAT IS DESCRIBED IN THIS ANNOUNCEMENT HAS NOT YET COMMENCED.
  ONCE THE TENDER OFFER COMMENCES, WE WILL FILE A SOLICITATION/RECOMMENDATION
  STATEMENT WITH THE SECURITIES AND EXCHANGE COMMISSION. YOU SHOULD READ THIS
  DOCUMENT WHEN IT BECOMES AVAILABLE BECAUSE IT WILL CONTAIN IMPORTANT INFORMATION
  ABOUT THE TENDER OFFER. YOU CAN OBTAIN THE SOLICITATION/RECOMMENDATION STATEMENT
  AND OTHER
  
                                       -more-
  
  
  <PAGE>
  
  
  
  DOCUMENTS THAT WILL BE FILED WITH THE SECURITIES AND EXCHANGE COMMISSION FOR
  FREE WHEN THEY ARE AVAILABLE ON THE SECURITIES AND EXCHANGE COMMISSION'S WEB
  SITE AT http://www.sec.gov. ALSO, IF YOU WRITE US OR CALL US, WE WILL SEND YOU
  THE SOLICITATION/RECOMMENDATION STATEMENT FOR FREE WHEN IT IS AVAILABLE.
  
  YOU CAN CALL US AT (781) 622-1111 OR WRITE TO US AT:
  
           INVESTOR RELATIONS DEPARTMENT
           THERMEDICS DETECTION INC.
           81 WYMAN STREET, P.O. BOX 9046
           WALTHAM, MA 02454-9046
  
  The following constitutes a "Safe Harbor" statement under the Private Securities
  Litigation Reform Act of 1995: This press release 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" included in Exhibit 13 to the company's annual report on Form 10-K
  for the year ended January 2, 1999. These include risks and uncertainties
  relating to: the market's acceptance of new products, the company's ongoing
  product development efforts required by rapid technological change, the
  dependence of the security-instrument market on government regulation and the
  airline industry, the significance of certain customers to the company, as well
  as risks associated with competition, potential product liability, international
  operations, proprietary technology rights, the company's acquisition strategy,
  potential fluctuations in quarterly performance, and the potential impact of the
  year 2000 on processing date-sensitive information.
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text: 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):
  
                                  January 31, 2000
                               ----------------------
  
                              THERMEDICS DETECTION INC.
                            ----------------------------
               (Exact name of Registrant as specified in its charter)
  
  Massachusetts                      1-12745                            04-3106698
  --------------------------------------------------------------------------------
  (State or other                  (Commission                    (I.R.S. Employer
  jurisdiction of                  File Number)             Identification Number)
  incorporation or
  organization)
  
  220 Mill Road
  Chelmsford, Massachusetts                                             01824-4178
  --------------------------------------------------------------------------------
  (Address of principal executive offices)                              (Zip Code)
  
                                   (781) 622-1000
                           (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" included in Exhibit 13
  to Thermedics Detection Inc.'s Annual Report on Form 10-K for the year ended
  January 2, 1999. These include risks and uncertainties relating to: the market's
  acceptance of new products, the Registrant's ongoing product development efforts
  required by rapid technological change, the dependence of the
  security-instrument market on government regulation and the airline industry,
  the significance of certain customers to the Registrant, as well as risks
  associated with competition, potential product liability, international
  operations, proprietary technology rights, the Registrant's acquisition
  strategy, potential fluctuations in quarterly performance, and the potential
  impact of the year 2000 on processing date-sensitive information.
  
  Item 5.  Other Events
           ------------
  
           On January 31, 2000, the Registrant issued a press release, attached
  hereto as Exhibit 99, regarding certain corporate transactions affecting the
  Registrant.
  
  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
  
                    99 Press Release dated January 31, 2000.
  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 31st day of January, 2000.
  
                                                   THERMEDICS DETECTION INC.
  
                                                   By:/s/ Theo Melas-Kyriazi
                                                      ---------------------------
                                                          Theo Melas-Kyriazi
                                                          Chief Financial Officer
  Exhibit 99
  Investor Contact: 781-622-1111
  Media Contact: 781-622-1252
  
                         THERMEDICS DETECTION ANNOUNCES CASH
                             TENDER OFFER BY THERMEDICS
  
  CHELMSFORD, Mass., January 31, 2000 - Thermedics Detection Inc. (ASE-TDX), a
  Thermo Electron company (NYSE-TMO), announced today that its parent company,
  Thermedics Inc. (ASE-TMD), will make a cash tender offer for any and all of the
  outstanding shares of Thermedics Detection common stock at $8.00 per share. This
  action is part of a major reorganization plan under which Thermo Electron will
  spin in, spin off, and sell various businesses to focus solely on its core
  measurement and detection instruments business.
  
           Thermedics currently owns approximately 83.6 percent of the outstanding
  shares of Thermedics Detection common stock. Thermedics will condition the
  tender offer on receiving acceptances from holders of enough shares so that,
  when combined with its current share ownership, Thermedics' ownership reaches at
  least 90 percent. If Thermedics achieves this 90-percent-ownership threshold, it
  will acquire all remaining outstanding shares of Thermedics Detection common
  stock through a "short-form" merger in Massachusetts. Shareholders who do not
  tender shares to Thermedics during the tender offer would also receive $8.00 per
  share in cash for their stock in the short-form merger.
  
           Thermo Electron, which owns approximately 5.3 percent of the
  outstanding shares of Thermedics Detection common stock, will tender its shares
  to Thermedics in the tender offer.
  
           The tender offer and proposed subsequent short-form merger require
  Securities and Exchange Commission clearance of necessary filings; a short-form
  merger would not require Thermedics Detection board or shareholder approval.
  
           The Thermedics board of directors has approved pursuing this proposed
  tender offer and short-form merger in lieu of continuing negotiations over a
  merger price with the Thermedics Detection special committee of its board of
  directors.
  
           Thermedics plans to conduct the tender offer during the second quarter
  of 2000. If Thermedics successfully obtains ownership of at least 90 percent of
  the outstanding Thermedics Detection shares, it expects to complete the spin-in
  by the end of the second quarter of 2000.
  
           Thermedics Detection develops, manufactures, and markets high-speed
  systems used for product quality assurance in a variety of industrial and
  laboratory processes, as well as for security at airports, border crossings, and
  other checkpoints. More information is available on the Internet at
  http://www.thermo.com/subsid/tdx1.html.
  
  OTHER IMPORTANT INFORMATION:
  THE TENDER OFFER THAT IS DESCRIBED IN THIS ANNOUNCEMENT HAS NOT YET COMMENCED.
  ONCE THE TENDER OFFER COMMENCES, WE WILL FILE A SOLICITATION/RECOMMENDATION
  STATEMENT WITH THE SECURITIES AND EXCHANGE COMMISSION. YOU SHOULD READ THIS
  DOCUMENT WHEN IT BECOMES AVAILABLE BECAUSE IT WILL CONTAIN IMPORTANT INFORMATION
  ABOUT THE TENDER OFFER. YOU CAN OBTAIN THE SOLICITATION/RECOMMENDATION STATEMENT
  AND OTHER
  
                                       -more-
  DOCUMENTS THAT WILL BE FILED WITH THE SECURITIES AND EXCHANGE COMMISSION FOR
  FREE WHEN THEY ARE AVAILABLE ON THE SECURITIES AND EXCHANGE COMMISSION'S WEB
  SITE AT http://www.sec.gov. ALSO, IF YOU WRITE US OR CALL US, WE WILL SEND YOU
  THE SOLICITATION/RECOMMENDATION STATEMENT FOR FREE WHEN IT IS AVAILABLE.
  
  YOU CAN CALL US AT (781) 622-1111 OR WRITE TO US AT:
  
           INVESTOR RELATIONS DEPARTMENT
           THERMEDICS DETECTION INC.
           81 WYMAN STREET, P.O. BOX 9046
           WALTHAM, MA 02454-9046
  
  The following constitutes a "Safe Harbor" statement under the Private Securities
  Litigation Reform Act of 1995: This press release 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" included in Exhibit 13 to the company's annual report on Form 10-K
  for the year ended January 2, 1999. These include risks and uncertainties
  relating to: the market's acceptance of new products, the company's ongoing
  product development efforts required by rapid technological change, the
  dependence of the security-instrument market on government regulation and the
  airline industry, the significance of certain customers to the company, as well
  as risks associated with competition, potential product liability, international
  operations, proprietary technology rights, the company's acquisition strategy,
  potential fluctuations in quarterly performance, and the potential impact of the
  year 2000 on processing date-sensitive information.