Adjuvant immunochemotherapy using Schizophyllan (SPG), an extract from the culture broth of Schizophyllum commune Fries, was prescribed at random for 326 Japanese patients with resectable gastric cancer. The overall survival rates for 3 years did not differ between the SPG and control groups. In 62 patients with stage I gastric cancer and 67 with stage II, there was little difference in the 3-year survival rates. The survival rates for 100 patients with stage III were enhanced at p = 0.0811 in the SPG group, as compared to the controls. The survival rates in 97 patients with stage IV cancer were much the same. These results warrant further application of this immunopotentiating drug for treating patients with resectable gastric cancer.