In order to evaluate the efficacy of combined immunochemotherapy with mitomycin-C, tegafur, PSK and/or OK-432 as an adjunct for curatively resected gastric cancer, a prospective randomized controlled study using the envelope method was performed, in which 266 institutions from around Japan participated. The 3 year survival rates for all cases, and for ps(+).n(+) cases, were insignificantly higher in the immunochemotherapy groups receiving PSK and/or OK-432 than in the control group. However, because 28.2 per cent of the cases were excluded from the final statistical analyses, the results of this study may have questionable statistical credibility. Changes in the stimulation index (SI) suggest that the administration of PSK may result in an inhibition of the immunosuppressive activity of cancer patients. The high SI group showed a significantly higher 4 year survival rate than the low SI group.