14C-labelled 4-methyl-5(2-pyrazinyl)-1,2-dithiole-3-thione (14C-oltipraz, 35 972 R.P.) was orally administered to rhesus monkeys (20 mg/kg), rats (50 mg/kg) and female mice infected with Schistosoma mansoni (100 and 250 mg/kg). The absorption of oltipraz varied with the animal species and the dose administered. In each species, the pharmacokinetics of oltipraz in the plasma and red blood cells were generally similar. 40 to 57% of the radioactive dose was excreted in urine, depending on the animal species and dose levels. In the mouse, there was negligible elimination of radioactivity as 14CO2. Whole-body autoradiographic studies in mice showed that, during the first 24 h, radioactivity was present mainly in the gastro-intestinal tract, bile, urine, liver and kidneys. In the male and female worms, the nature and amounts of radioactive products present differed.