The metabolism of dimethylarsinic acid (DMA) a common pesticide and the main metabolite of inorganic arsenic in mammals, has been studied in mice, hamsters and man. Mice and hamsters were administered a single dose of 74As-DMA (40 mg As/kg body weight) orally, while a human subject ingested DMA corresponding to 0.1 mg As/kg body weight. Ion exchange chromatography, paper electrophoresis, thin layer chromatography as well as arsine generation--gas chromatography combined with atomic absorption spectrophotometry or mass spectrometry were used to characterize the arsenic metabolites in urine and feces collected over 48 hours after treatment. In mice and hamsters 3.5% and 6.4% of the dose, respectively, were excreted in urine in the form of trimethylarsine oxide (TMAO). No TMAO was found in feces. A DMA-complex was detected in urine and feces. It amounted to about 13% of the dose in mice and 15% in hamsters. About 80-85% of the dose was eliminated in urine and feces in the form of unmetabolized DMA. No demethylation of DMA to inorganic arsenic was observed. In man, about 4% of the dose was excreted in urine as TMAO and about 80% as DMA.