The Gastric Cancer Immunochemotherapy Study Group, constituted of 412 institutions, carried out six independent trials simultaneously from 1978 to 1981. A total of 4,456 cases were subjected to the study, from which 826 cases (18.5%) were excluded due to the violence of entry criteria. Curative gastrectomy, followed by a combination of mitomycin C (MMC), Ftorafur (FT)and Krestin (PSK) produced better postoperative survivals than either combination of MMC and FT, or MMC and PSK (5-year survival rate: 71.7% in MMC + FT + PSK, 64.1% in MMC + PSK, and 58.5% in MMC + FT). In the subset of patients with negative nodes (n(-)), and with involved serosa by histological examination (ps(+)), a combination of FT and PSK after gastrectomy seemed to be more favorable for the post-operative survivals than the single use of either drug. Four drug combinations of MMC, FT, PSK and Picibanil (OK-432) also had a clinical benefit in the group of patients with poorly differentiated adenocarcinoma, compared with chemotherapy alone. These results, though there are biases due to excluding 18.5% of cases, suggest some clinical benefits in the control of cancer relapse after surgery. The conclusion should be confirmed by a further elaborate trial.