2-Thiothiazolidine-4-carboxylic acid (TTCA) was measured in urine of two persons given an oral dose of 250 mg disulfiram. Maximum concentrations up to 0.33 mmol TTCA/mol creatinine were found, 10 to 14 h after dosing. The total amounts of TTCA excreted in urine were 1.8 and 3.5 mumol, respectively, which correspond to 0.2 and 0.4% of the dose.