Personal monitoring of exposure to tetrachloroethylene (TETRA) with carbon felt dosimeters and analyses of urine for total trichloro-compounds (TTC) were carried out in two groups of workers (36 males and 25 females), one group (20 males and 19 females) in dry-cleaning workshops and the other (16 males and 6 females) engaged in the removal of glue from silk cloth. Comparison of the urinary TTC levels with TETRA in the environment revealed that, while the metabolite levels increased essentially linear to TETRA concentrations up to 100 ppm, leveling off was apparent in the metabolite excretion when the exposure to TETRA was more intense (e.g. more than 100 ppm), indicating that the capacity of humans to metabolize TETRA is rather limited, as previously discussed. From the set of the data thus obtained, screening levels of 30 and 61 mg TTC (as TCA)/l urine as the lower 95% confidence limits for a group mean were calculated for the biological monitoring, by means of urinalysis, of exposure to TETRA at 50 and 100 ppm (TWA), respectively. A tentative calculation with additional exhaled-air analyses indicated that, at the end of an 8-h shift with exposure to TETRA at 50 ppm (TWA), 38% of the TETRA absorbed through the lungs would be exhaled unchanged and less than 2% would be metabolized to be excreted into the urine, while the rest would remain in the body to be eliminated later.