The aim of this study was to measure the tissue concentration of anti-cancer agents administered by arterial infusion. After the abdominal cavity was opened, 250 mg of 5-FU diluted in 20 ml saline was infused into the feeding artery in 16 patients with colonic cancer. After the affected lesion was resected, specimens were obtained at the tumor, at sites 5 and 10 cm from the center of the tumor, and at the adjacent nodes. The concentration of 5-FU was higher in the tumor and the adjacent lymph nodes than in the normal colon near the lesion. This suggests that 5-FU has a more favorable distribution profile in tumor tissue than in normal tissue. Patients with a high concentration of 5-FU in the tumor also demonstrated high levels in the other tissue. Blood flow volume and the length of time between the injection of 5-FU and harvest of the specimen may account for differences in the tissue concentration of the agent after administration of the same dose.