After a single or seven consecutive daily oral administration of pyraclofos ((R,S)-[O-1-(4-chlorophenyl)pyrazol-4-yl O-ethyl S-propyl phosphorothioate], Boltage((R)) labeled with C-14 at the benzene ring to male and female rats at the rate of 5 mg/kg, radioactivity (C-14) excreted into the urine, feces and expired air in 7 days was 87-95%, 4-5% and less than 0.1%, respectively. The major excretion route was urine. C-14 in the blood of both sexes reached maximum 4 hr after administration, and the concentration was relatively high in the liver, kidney and lung. C-14 in the brain and spinal cord was extremely low, and there was no accumulation of C-14 in the specific tissues 7 days after both single and seven consecutive daily administration. Six metabolites were identified in the urine and feces: 1-(4-chlorophenyl)-4-hydroxypyrazole (CHP), sulfate conjugation of CHP, 1-(4-chlorophenyl)pyrazol-4-yl S-propyl hydrogen phosphorothioate, 1-(4-chlorophenyl)pyrazol-4-yl O-ethyl hydrogen phosphorothioate, O-ethyl S-propyl hydrogen phosphorothioate and O-ethyl phosphoric acid. The amount of the parent compound was in both urine and feces. Major metabolic pathways of pyraclofos were cleavage of P-O-aryl, P-O-alkyl and P-S-alkyl bonds, and conjugation of CHP with sulfuric acid.