The urinary excretion of mercapturates was followed photometrically in individuals exposed to styrene, a mixture of aromatic hydrocarbons, butadiene, vinyl chloride, 1,1,1-trichloroethane, trichloroethylene, tetrachloroethylene, 1,1,1-trifluoro-2-bromo-2-chloroethane (Halothane), ethylene oxide, epichlorhydrin, bis(chloromethyl)-ether, N-methylacrylamide, dimethylformamide, nitrosamines or cis-platinum and in groups of controls, smokers and nonsmokers, males and females, the residents of city P, industrial town V.M. and mountain village S. The increase in the urinary excretion of mercapturates was found in individuals exposed to styrene, aromatic hydrocarbons, dimethylformamide, 1,1,1-trichloroethane, and in smokers. In groups of controls, the lowest mercapturate concentrations were detected in the urine samples of nonsmokers from the mountain village S. where the degree of air pollution due to motor vehicle emissions was lowest at the time of investigation.