Our main objective was to describe the metabolism of dithiobiuret (DTB) in the adult, male rat. Based on the thin-layer chromatographic analysis of urine from animals treated ip with 1 mg/kg of [14C] or [35S] labeled DTB, two pathways for metabolism are proposed. One pathway is reversible and involves the oxidation of DTB to thiuret and the reduction of thiuret back to DTB. The other pathway consists of the desulfuration of DTB to monothiobiuret. The liver appears to desulfurate DTB because DTB-derived [35S] was eliminated from the liver more rapidly (T1/2 = 10 hr) than [14C] (T1/2 = 15 hr). The liver was the only tissue where the elimination kinetics of [35S] and [14C] DTB were different. For all extrahepatic tissues examined and plasma, the elimination of DTB-derived [35S] paralleled that of [14C]. The T1/2 for plasma disappearance of both radiolabeled forms of DTB was approximately 10 hr and the cumulative urinary excretion of DTB-derived [35S] and [14C] was parallel and amounted to about 60% of the dose in 24 hr. DTB-derived radioactivity in urine that co-chromatographed with DTB, monothiobiuret, thiuret and sulfate was quantitated along with that of three uncharacterized metabolites. The presence of these unknown metabolites suggests that DTB metabolism is complex. The present study is the first description of the metabolic fate of DTB in the rat and serves as a starting point for determining whether DTB neurotoxicity is caused by the parent compound or a metabolite.