The metabolic fate of disulfiram labeled with both 14C and 35S was studied in the rat. After administration of 50 mg of 14C, 35S-disulfiram dissolved in corn oil to rats by stomach tube, 95% of the radioactivity was recovered in urine, feces, and expired air at 144 hr. The major portion of the excreted radioactivity was in urine (75 +/- 6%). Feces and expired air contained 13 +/- 2% and 6 +/- 5% of the body organs or carcass. Pretreatment of rats with unlabeled disulfiram for 20 days prior to administration of 14C, 35S-disulfiram led to more rapid catabolism of the drug and more rapid excretion of radioactivity in the urine during the first 12 hr after dosing.