Trichloroethylene was oxidized by purified toluene dioxygenase obtained from recombinant E. coli strains. The major oxidation products were formic acid and glyoxylic acid. Other potential products, dichloroacetic acid, chloral, phosgene, carbon monoxide, and carbon dioxide, were not detected. [14C]trichloroethylene became covalently attached to protein components and NADPH suggesting non-specific alkylation by reactive products. Oxidation of deuterated trichloroethylene yielded 50.2% deuterated formate. Oxidation of trichloroethylene in D2O yielded 43.7% deuterated formate. These data indicate that both carbon atoms are giving rise to formic acid. The results are consistent with a mechanism of TCE oxygenation not involving epoxide, dioxetane, or dihydroxy intermediates and indicate significant differences from those previously proposed for cytochrome P-450 (Miller, R.E. & Guengerich, F.P. (1982) Biochemistry 21, 1090-1097) or methane monooxygenase (Fox, B.G., Borneman, B.G., Wackett, L.P., & Lipscomb, J.D. (1990) Biochemistry 29, 6419-6227).