Mercapturic acid derivatives or other thioethers can be considered as the endproducts of the metabolic detoxification of possibly alkylating agents. It is proposed that the appearance of these metabolites in the urine can be used as an indicator of exposure of the organism to such toxic compounds. A simple, practical procedure for determination of thioethers in urine samples is described. Employees of chemical and metal industries have been compared with respect to their urinary thioether concentrations. It was found that chemical workers excreted more thioether compounds than persons engaged in metal industry.