A compound was isolated from the urine of workers exposed to carbon disulfide during the production of rayon. The compound was identified as 2-thiothiazolidine-4-carboxylic acid (TTCA) by GC/MS and NMR. A HPLC method for the quantitative determination of TTCA was elaborated and applied to urine samples. The method allowed detection of TTCA concentrations in urine as low as 5 X 10(-7) M. No TTCA was detected in urine of workers occupationally exposed to organic solvents other than CS2. High concentrations of TTCA (upto 32 X 10(-5) M) were shown to be present in urine of spinners exposed to CS2 concentrations of approximately 100 mg/m3. It is suggested that the assay of urinary TTCA is suitable for detection of occupational exposure to CS2.