The chemical nature and magnitude of [ 14 C]malathion residues in the milk, eggs (whites and yolks), fat, liver, kidney, and muscle tissues in dairy goats and laying hens were examined after repeated oral exposure. The level and duration of the dose given to goats were equivalent to 86 ppm on feed for 5 days. Chickens received the equivalent of 28 ppm on feed for 4 days. Radioactive residues were characterized and identified using solvent extraction and chromatography. The parent chemical was not detectable, and immediate metabolites of malathion were not present in any tissues except traces of the mono-and dicarboxylic acid metabolites observed in goat kidney. This observation was consistent with urinary excretion as the major elimination pathway of malathion and immediate metabolites in poultry, laboratory animals, and humans. Extensive degradation and metabolism resulted in the reincorporation of the radiolabel into normal biogenic chemicals in all investigated samples. The products were typical of those derived from the tricarboxylic acid cycle. The products included pyruvate, lactate, lactose, oleic acid, stearic acid, and glycerol. Reincorporation of radiolabel into protein was also demonstrated by the isolation and hydrolysis of casein from milk. It was concluded that ingested malathion was converted to acetate or other volatile fatty acids, metabolized to acetyl-CoA, and then incorporated into the carbon pool.