From July 1977, a controlled clinical trial in 168 patients who received curative surgery for stomach cancer and 111 similarly treated for colorectal cancer was conducted in the form of a cooperative study involving 22 institutions. One week after surgery, carboquon (CQ) was given at a dose of 2 mg/m2 once a week, followed by PSK at a dose of 2 g/m2 every day for 4 weeks. This regimen was repeated 9 times for 55 weeks. For stomach cancer, patients were divided into 3 groups; Group A: CQ intermittently, Group B: CQ PSK in alternate doses, Group C: controls. For colorectal cancer, the patients were divided into 2 groups; Group D: CQ + PSK in alternate doses, Group E: controls. Survival rate of stage III stomach cancer patients in Group B was higher than that in Group A, the difference being statistically significant between 20 and 24 months after surgery. For colorectal cancer, the survival rate of patients with Dukes C in Group D was statistically superior to that in Group E. These differences were much more apparent among patients who received more than 6 courses of the regimen.