In collaboration with 428 institutions nation-wide, comparative studies on the optimal daily dosage of UFT were carried out for non-curative resection cases of colorectal cancer for two years from January 1984 to December 1985. The administration method employed was as follows. Group C received 12 mg/m2 of MMC on the day of operation, followed by 6 mg/m2 every 2 months 6 times, and from the 2nd week after the operation 600 mg/body of UFT was continuously administered every day for 1 year. Group D received 400 mg/body of UFT every day and the same amount of MMC as Group C. Analysis was made of 556 evaluable cases. There was no difference in the survival rate between the two groups. With respect to the dosage per body weight (kg), 8-12 mg/kg of UFT produced good prognoses and less side effects than the group which received more than 12 mg/kg. It seems necessary to administer UFT at its optimal dosage for colorectal cancers.