Immunochemotherapy using the antitumor polysaccharide Sizofiran (SPG), an extract from the culture broth of Schizophyllum, was prescribed randomly for unresectable or resectable gastric cancer patients. In case of unresectable cases, the SPG group (treated by SPG plus tegafur--F method--or 5-FU combined with MMC--MF method--) survived longer (p = 0.009 in the MF method and p = 0.003 in the F method) than did the control group (chemotherapy only). Concerning a treatment regimen for resectable cases, all patients were given 0.4mg/kg and 0.2mg/kg of MMC on the day of surgery and the next day, respectively. Oral tegafur was initiated on the 14th postoperative day and was continued as long as possible. In the SPG group, SPG was administered intramuscularly 40mg/week concurrently with the start of oral tegafur and was continued as long as possible. Although the overall survival rates for 5 years did not differ between both groups, the 5-year survival rate for stage III in the SPG group was superior to the findings for stage III in the control (p = 0.0105).