The pharmacokinetics of 3, 4-dihydro-6-[4-(3,4- dimethoxybenzoyl )-1-piperazinyl]-2(1H)- quin olinone ( OPC -8212) were studied after the administration of 14C- OPC -8212 or OPC -8212 to animals of different species. After oral doses of 10 mg/kg of 14C- OPC -8212 to rats and beagle dogs, the Tmax, Cmax and T1/2 values of OPC -8212 were 4 h, 2995 ng eq/ml, and 3-4 h in rats and 1 h, 2244 ng eq/ml and 5-6 h in beagle dogs, respectively. After oral doses of 10 mg/kg of 14C- OPC -8212 to rats, the radioactivity was distributed comparatively widely in the tissues. However, there was no evidence of accumulation of radioactivity in the tissues due to repeated oral doses of 10 mg/kg of 14C- OPC -8212 once a day for 21 days. After oral doses of 10 mg/kg of 14C- OPC -8212, the amounts of radioactivity excreted in the urine and feces in the first 72 h accounted for 29.25% and 60.24% of the dose in rats and 35.53% and 63.18% of the dose in beagle dogs, respectively. There were no apparent changes in the urinary and fecal excretions of radioactivity due to repeated oral doses of 10 mg/kg of 14C- OPC -8212 once a day for 21 days in rats. Biliary excretion of radioactivity was 22.41% of the dose after oral doses of 10 mg/kg 14C- OPC -8212 in rats. Enterohepatic circulation was 22.04% of the dose after an intraduodenal dose in rats.(ABSTRACT TRUNCATED AT 250 WORDS)