In order to evaluate the clinical effectiveness of immunotherapy on gastric cancer patients, we performed two controlled trials of immunotherapy with BCG-CWS and Nocardia rubra CWS respectively. A controlled trial of BCG-CWS was performed from 1976 to 1978. The result showed an improved survival rate of the immunotherapy as compared with the chemotherapy group. From September 1979 through March 1981, a total of 302 patients with gastric cancer undergoing gastrectomy at the Department of Surgery, Chiba University Hospital and its 14 affiliated hospitals were studied for clinical effectiveness of immunotherapy with N-CWS. The subjects were stratified by a gross stage of cancer and degree of operative curability. They were then randomly assigned to either chemotherapy group or chemotherapy plus immunotherapy group. Immunotherapy used was intradermal injection of 400 micrograms of N-CWS which was given weekly for the first month and monthly thereafter. After the specimen was examined microscopically, the patients were classified by histological stage of cancer and radicality of surgical intervention into curative or non-curative groups. The patients were surveyed for survival period in December 1981. No statistical difference was found between the two treatment groups in age, sex or operative procedures that might influence the patient's survival. As a result, statistical intergroup difference in survival rates was not seen in patients of the curative group, probably due to short observation period. However, the intergroup difference in survival rates was statistically significant in patients of the non-curative group (p less than 0.01). These results indicate that the immunotherapy with BCG-CWS or with N-CWS is effective in patients undergoing gastrectomy for gastric cancer.