Correlation between 5-FU (20mg/kg) administrated via the peripheral vein and tissue concentration of its metabolite was studied in hepatic metastasis model prepared for rats. The measurement of tissue samples collected 30 min. after the 5-FU administration suggested a possible negative correlation between the F-dUMP concentration and the blood flow in the normal hepatic tissue of the control group and the tumor tissue in the metastasis group. In administering 5-FU, a time-dependent anticancer drug, to the tumor rich in the tissue blood flow, washing-off effect of the drug by blood outflow cannot be neglected. Some device of prolonging the exposure time of anti-cancer agent to the tumor tissue will be necessary.