Exhibit 21 THERMO TERRATECH INC. Subsidiaries of the Registrant As of May 23, 1997, Thermo TerraTech Inc. owned the following companies: STATE OR JURISDICTION PERCENT NAME OF OF INCORPORATION OWNERSHIP Thermo TerraTech Inc. Delaware CarlanKillam Consulting Group, Inc. Florida 100 Carlan Consulting Group of Alabama, Inc. Alabama 100 CarlanKillam Construction Services, Inc. Florida 100 Holcroft (Canada) Limited Canada 100 Holcroft Corporation Delaware 100 Holcroft GmbH Germany 100 Metallurgical, Inc. Minnesota 100 Cal-Doran Metallurgical Services, Inc. California 100 Metal Treating Inc. Wisconsin 100 Normandeau Associates, Inc. New Hampshire 100 The Randers Group Incorporated Delaware 53.3 (additionally, 8.9% of the shares are owned directly by Thermo Electron Corporation) Randers Engineering, Inc. Michigan 100 Clark-Trombley Consulting Michigan 100 Engineers, Inc. Redeco Incorporated Michigan 100 Randers Group Property Michigan 100 Corporation Viridian Technology, Inc. Michigan 100 Randers - EPC Incorporated Illinois 100 Randers Engineering of Michigan 100 Massachusetts, Inc. Thermo Analytical Inc. Delaware 100 Skinner & Sherman, Inc. Massachusetts 100 Thermo Consulting & Design Inc. Delaware 100 Engineering Technology and Knowledge Delaware 100 Corporation Elson T. Killam Associates, Inc. New Jersey 100 BAC Killam Inc. New York 100 N. H. Bettigole Co., Inc. Delaware 100 N. H. Bettigole, P.A. New Jersey 100 N. H. Bettigole, P.C. New York 100 Duncan, Lagnese and Associates, Pennsylvania 100 Incorporated E3-Killam, Inc. New York 100 Killam Associates, Inc. Ohio 100 Killam Management and Operational New Jersey 100 Services, Inc. Fellows, Read & Associates, Inc. New Jersey 100 Killam Associates, New England Inc. Delaware 100 Page 1PAGE Exhibit 21 THERMO TERRATECH INC. Subsidiaries of the Registrant STATE OR JURISDICTION PERCENT NAME OF OF INCORPORATION OWNERSHIP George A. Schock & Associates, Inc. New Jersey 100 Jennison Engineering, Inc. Vermont 100 Thermo EuroTech N.V. Netherlands 53.25 Grond- & Watersaneringstechniek Netherlands 100 Nederland B.V. Refining & Trading Holland B.V. Netherlands 100 Thermo Remediation Inc. Delaware 68.92 (additionally, 1.48% of the shares are owned directly by The Thermo Electron Companies Inc.) Eberline Holdings Inc. Delaware 100 Eberline Analytical Corporation New Mexico 100 Thermo Hanford Inc. Delaware 100 TMA/NORCAL Inc. California 100 IEM Sealand Corporation Virginia 100 Remediation Technologies, Inc. Delaware 100 RETEC Thermal, Inc. Delaware 100 ReTec/Tetra L.C. Texas 50* TriTechnics Corporation Colorado(?) 100 Thermo Fluids Inc. Delaware 100 TPS Technologies Inc. Florida 100 TPST Soil Recyclers of California Inc. California 100 California Hydrocarbon, Inc. Nevada 100 TPST Soil Recyclers of Maryland Inc. Maryland 100 Todds Lane Limited Partnership Maryland 100* (1% of which is owned directly by TPS Technologies Inc.) TPST Soil Recyclers of New York Inc. New York 100 TPST Soil Recyclers of Oregon Inc. Oregon 100 TPST Soil Recyclers of South Carolina Delaware 100 Inc. TPST Soil Recyclers of Virginia Inc. Delaware 100 TPST Soil Recyclers of Washington Inc. Washington 100 TMA/Hanford, Inc. Washington 100 Thermo Securities Corporation Delaware 100 Thermo Soil Recyclers Inc. Massachusetts 100 Thermo Technology Ventures Inc. Idaho 100 Plasma Quench Investment Limited Delaware 60* Partnership * Joint Venture/Partnership