UFT is a preparation consisting of tegafur and uracil at the molar ratio 1 : 4. In 22 resected patients with hepatocellular carcinoma (HCC), the concentrations of 5-fluorouracil (5-FU), tegafur and uracil were estimated in the serum, liver and cancer tissues after oral administration of UFT (tegafur, 300mg) before operation. The concentrations of 5-FU, tegafur and uracil in the serum were highest at 2 hours, and reduced thereafter. The maximum 5-FU level was 0.040 +/- 0.034 microgram/ml. The concentrations of 5-FU in the cancer tissue were 0.101 +/- 0.070 microgram/g in all patients, 0.085 +/- 0.050 microgram/g in cirrhotic patients and 0.144 +/- 0.105 microgram/g in non-cirrhotic patients. These concentrations were significantly higher than those in the liver tissue. In 10 out of 13 patients, 5-FU concentrations was higher than 0.056 microgram/g which was reported as minimum effective concentration. CONCLUSIONS the concentration of 5-FU after oral administration of UFT prior to resection of HCC was estimated in the serum, liver and cancer tissues. The concentration of 5-FU in cancer tissues was satisfactorily higher regardless of cirrhotic or non-cirrhotic conditions UFT seemed to be a safe and useful drug since tissue 5-FU concentration was higher than those in the serum and liver.