Exhibit 21 THERMO OPTEK CORPORATION Subsidiaries of the Registrant At February 28, 1997, the Registrant owned the following companies: Registrant's State of Jurisdiction % of Name or Incorporation Ownership --------------------------------------------------------------------------- ARL Applied Research Laboratories S.A. Switzerland 100 Fisons Instruments (Proprietary) Limited South Africa 100 Thermo Optek Wissenschaftliche Gerate GesmbH Austria 100 Fisons Instruments Inc. Canada 100 Fisons Instruments Nordic AB Sweden 100 ATI Acquisition Corp. Wisconsin 100 Mattson Instruments Limited United Kingdom 100 Thermo Elemental Limited United Kingdom 100 Unicam Analytical Inc. Canada 100 Unicam Analytical Technology Netherlands B.V. The Netherlands 100 Unicam Italia SpA Italy 100 Unicam S.A. Belgium 100 Thermo Optek Limited United Kingdom 100 Unicam Limited United Kingdom 100 Unicam Export Limited United Kingdom 100 Nicolet Instrument Corporation Wisconsin 100 Nicolet Japan K.K. Japan 100 Spectra-Tech, Europe Limited United Kingdom 100 Spectra-Tech, Inc. Wisconsin 100 Nicolet Instrument GmbH Germany 100 Optek Securities Corporation Massachusetts 100 Thermo Instrument Systems Japan Holdings, Inc. Delaware 100 Nippon Jarrell-Ash Company, Ltd. Japan 100 Thermo Jarrell Ash Corporation Massachusetts 100 Baird Do Brazil Representacoes Ltda. Brazil 100 Beijing Baird Analytical Instrument Technology Co. Limited China 100 Thermo Instrument Systems (F.E.) Limited China 100 Thermo Instruments (Canada) Inc. Canada 100 Eberline Instruments (Canada) Ltd. Canada 100 Thermo Optek France S.A. France 100 PAGE Exhibit 21 THERMO OPTEK CORPORATION Subsidiaries of the Registrant (continued) Registrant's State of Jurisdiction % of Name or Incorporation Ownership --------------------------------------------------------------------------- Planweld Holding Ltd. United Kingdom 100 Nicolet Instrument Limited United Kingdom 100 Planweld Limited United Kingdom 100 Hilger Analytical Limited United Kingdom 100 Thermo Electron Limited United Kingdom 100 Thermo Optek Holding B.V. The Netherlands 100 Baird Europe B.V. The Netherlands 100 Baird France S.A.R.L France 100 Thermo Group B.V. The Netherlands 100 Thermo Vision Corporation Delaware 100 CID Technologies Inc. New York 100 Laser Science, Inc. Delaware 100 Oriel Instruments Corporation Delaware 100 Oriel Foreign Sales Corp. U. S. Virgin Islands 100 Scientific Measurement Systems Colorado 100