14C-diphacinone (0.2-1.5 mg/kg) was orally administered to rats and mice. Residue distribution in various tissues and radiocarbon elimination in feces and urine were determined. More than 60% of the administered radiocarbon was eliminated in feces and about 10% in urine in 4 days from mice and in 8 days from rats. The greatest amount of radioactivity in tissues of both rats and mice appeared in liver. Brain, muscle, blood, and fat had the lowest residue levels. Metabolites in feces and liver were chromatographically isolated and identified by mass spectrometry. In addition to unchanged diphacinone, four hydroxylated metabolites were identified in feces and liver. Hydroxylation occurred on either or both the indandione or phenyl rings. The positions of the hydroxy groups on the rings were not established.