For a period of about three years from September 1980, a randomized controlled study was performed on colo-rectal cancer patients who had undergone an absolute curative operation. After operation and administration of 30 mg of Mitomycin (20 mg on the day and 10 mg on the day following the operation), all patients were randomly divided into two groups which received the treatments as follows; Group A, 750 mg x 2/day of FT-207 suppositories, was administered for one year from the 2 nd week after operation; Group B was given FT-207 3.0 g/day of PSK orally for one year. Group A included 71 patients, of whom 46 had colon cancer and 25 had rectal cancer. Group B included 53 patients, of whom 30 patients had colon cancer and 23 had rectal cancer. There was no difference between the two groups in terms of patients' background factors. In regard to the 5-year survival rates of these patients by means of the Kaplan-Meier Method, Group A and B showed 80.8% and 91.4%, respectively, but no significant difference was observed. In the colon cancer patients, 5-year survival rates were 88.6% and 93.0% in Group A and B, and in the rectal cancer patients, they were 68.0% and 87.5% in Group A and B, respectively. The survival rate of Group B was always slightly higher than that of Group B in all analyses, in which we considered such factors as degree of progression, depth of cancer invasion of the wall, lymphnode metastases and vascular invasion. There were no differences between both groups in the patterns and times of recognition of the recurrences, but the number of cases evidencing recurrences within 2 years tended to be smaller in Group B. Thus, it was suggested that PSK was effective for prolongation of the survival period in colo-rectal cancer patients after absolute curative operation.