To evaluate the effect of immunochemotherapy starting in the early postoperative period for stage III gastric cancer, 330 patients after radical subtotal gastrectomy were randomly allocated to receive immunochemotherapy (n = 159), chemotherapy (n = 77) and surgery alone (n = 94). For immunotherapy, a Streptococcus pyogenes preparation (Picibanil) was administered intramuscularly with a dosage of 1.0 KE every week from the fourth or fifth postoperative day on. Mitomycin C 4 mg/50 kg and 5-Fluorouracil 500 mg/50 kg were given intravenously twice a week for the first two weeks, and then weekly for the next six weeks. Thereafter, oral 5-Fluorouracil (600 mg/50 kg) was given daily. Immunochemotherapy was continued for 24 months if possible. In all treatment groups, the immune status using skin tests, lymphocyte count and stimulation as well as cytotoxicity was investigated before an operation and at the third and fourth postoperative months. Five-year survival rates of groups 1, 2 and 3 were 45.3%, 29.8% and 24.4% respectively, the difference between the immunochemotherapy group and the other two groups being significant. All postoperative immune parameters showed more favorable values in the immunochemotherapy group. The data suggest that the postoperative adjuvant unspecific immunotherapy is able to prolong survival for stage III gastric cancer patients.