The serum and bile tegafur (FT), 5-fluorouracil (5-FU) and uracil levels after administration of UFT were assessed in 13 cases of malignant biliary tumor accompanied by biliary obstruction in comparison with FT alone. The serum and bile FT and 5-FU levels showed almost the same transition pattern in both groups, reaching to the plateau in 1-2 weeks and revealing cumulative effect by continual administration. Correlation was obtained between serum and bile levels except for 5-FU level in UFT group (p less than 0.05). Correlation between 5-FU and uracil was obtained in the serum in both groups (p less than 0.05), but no effect of uracil was observed. In bile, correlation was seen only in UFT group (p less than 0.05), and the effect of uracil was observed in bile 5-FU level.