Biological monitoring of occupational exposure to tetrachloroethene. Scand j work environ health 9 (1983) 273-281. In the breathing zone of 32 workers concentrations of tetrachloroethene were measured during five consecutive workdays. The feasibility of biological monitoring was tested by the measurement of the concentrations of tetrachloroethene in blood and exhaled air and the urinary excretion of trichloroacetic acid and trichloroethanol. The best parameter to estimate the time-weighted average exposure to tetrachloroethene over the whole workweek appears to be the concentration of both tetrachloroethene and trichloroacetic acid in blood 15-30 min after the end of the workday at the end of the workweek. Among the noninvasive methods the best parameter is the tetrachloroethene concentration in exhaled air 15-30 min after work at the end of the workweek, followed by the measurement of trichloroacetic acid in urine at the end of the workweek. In exposure to 2,050 pmol of tetrachloroethene/m3 (340 mg/m3, 50 ppm) the eshmated values for the biological parameters are 13.2 pmol of tetrachloroethenell of blood, 33 tun01 of trichloroacetic acidP of blood, 920 pmol of tetrachloroethenelm3 of exhaled air and 6.1 ymol of trichloroacetic acidlmmol of creatinine in urine, respectively. With 95 % confidence it may be stated that an individual with a value for a biological parameter not exceeding 8.3 pmol of tetrachloroethenell of blood, 20 pmol of trichloroacetic acid11 of blood, 515 pmol of tetrachloroethene/m3 of exhaled air and 3.0 ymol of trichloroacetic acidlmmol of creatinine, respectively, had an exposure not exceeding 2,050 pmol of tetrachloroethene/m3. The measurement of trichloroethanol in urine may be used for the estimation of the time-weighted average exposure over the previous 2 d. The concentration of tetrachloroethene in exhaled air 15-30 min after exposure had little value for the estimation of the time-weighted average exposure over the last 4 h. On Monday morning the concentration of tetrachloroethene in exhaled air is still about 15 % of the time-weighted average exposure concentration during the whole preceding workweek. The half-time of trichloroacetic acid in urine and blood during the weekend is about 65-90 h. K e y terms: metabolism, trichloroacetic acid, trichloroethanol. Tetrachloroethene(tetrachloroethylene, perchloroethylene) i s a volatile, nonflammable liquid widely used a s a degreasi n g a n d drycleaning solvent. T h e u p t a k e of tetrachloroethene by the lung is rather high (alveolar retention 60-80 %) (2,8) because of its high solubility i n blood a n d