The adequate flow volume and dose of 5-FU with the blood flow of proper hepatic artery in continuous hepatic infusion was investigated using young pig. The arterial blood flow of proper hepatic artery of pig per minute was 41.2 ml on average. 5-FU concentration was calculated in hepatic vein and peripheral vein during arterial infusion. When the speed and volume were put at 5 mg/kg/day and 5 ml/day, no 5-FU was recognized either in hepatic vein or peripheral vein. Also, at this low dose and flow volume, F-dUMP was recognized in liver tissue, and the thymidylate synthetase inhibition rate was 10-20%. From the standpoint that 5-FU is a time dependent drug effective for tumor cells only in the S-phase, continuous infusion of 5-FU will be much more effective than one-shot administration so as to prolong the presence of 5-FU even when the TS inhibition rate is low.