A Streptococcal preparation, OK-432, has been used for the treatment of cancer patients as a non-specific immunostimulant. According to the reports of many investigators, MFC (Mitomycin C, 5-Fluorouracil, Cytosine arabinoside) chemotherapy was effective in gastric cancer. Therefore, in this surdy, 77 gastric cancer patient were treated with OK-432 in combination with MFC chemotherapy. Immunological parameters, such as lymphocyte counts, T-cell counts, PHA blastformation rate and the PPD skin test, and the survival rate were examined to determine which was suitable for establishing the prognosis of cancer patients. The immunochemotherapy with OK-432 combined with MFC chemotherapy was effective in Stage III and Stage IV gastric cancer patients. Treatment with OK-432 prevented the depression of cell-mediated immunity induced by surgical intervention and administration anti-cancer agents. The immunotherapy with OK-432 enhanced the cell-mediated immunity of gastric cancer patients for 3 to 12 months after operation. However, elevation of the cell-mediated immunity was not detected more than 12 months after operation. It seemed that the immune status indicated by more than 3 out of the 4 immunological parameters reflected the cell-mediated immunity of gastric cancer patients. Moreover there was a statistically significant correlation between prognosis and the immune status of the patients. The long term prognosis of gastric cancer patients could be estimated by the values of the immunological parameters 3 months after operation. Neither over stimulation nor severe side effects were noted after long term administration of OK-432 to gastric cancer patients, and OK-432 seemed to be safe for use.