The excretion of tetrachloroethene metabolites in urine was studied in occupationally exposed workers to identify and quantify metabolites formed by glutathione conjugation and by cytochrome P450 oxidation of tetrachloroethene in humans. The glutathione conjugation pathway has been implicated in the chronic toxicity and possible tumorigenicity of tetrachloroethene to the kidney in rats. The biosynthesis of S-(1,2,2-trichlorovinyl)glutathione and N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine in humans had not been demonstrated. In this study, we investigated the biotransformation of tetrachloroethene in humans occupationally exposed during dry cleaning. Tetrachloroethene concentrations in the air of the dry cleaning shop were 50 +/- 4 ppm; two individuals were exposed for 8 hr daily and two individuals were exposed for 4 hr daily. In urine samples collected from the individuals at the beginning and at the end of the work week, N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine and 2,2,2-trichloroethanol as tetrachloroethene metabolites in humans were identified by GC/MS. The concentrations of N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine in the urine of the individuals were not significantly different at the start and at the end of the work week; however, concentrations of both N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine and 2,2,2-trichloro compounds (trichloroacetic acid and 2,2,2-trichloroethanol) as a marker for cytochrome P450-mediated metabolism were proportional to the length of daily tetrachloroethene exposure. A remarkable difference in the excretion pattern of 2,2,2-trichloro compounds, the major tetrachloroethene metabolites, was observed. Trichloroacetic acid and 2,2,2-trichloroethanol were present in the urine of two of the exposed individuals. Only 2,2,2-trichloroethanol was identified as a major urinary tetrachloroethene metabolite in two other individuals who did not excrete detectable amounts of trichloroacetic acid. The obtained results indicate that humans also have the ability to biosynthesize nephrotoxic glutathione S-conjugates from tetrachloroethene; however, when compared with rats, the human capacity for the biosynthesis of N-acetyl-S-(1,2,2-trichlorovinyl)-L-cysteine seems to be lower.