To clarify the clinical efficacy of SPG, a beta-1, 3 glucan extracted from cultured Schizophyllum commune Fries, a randomized comparative study was performed in combination with mitomycin C+5-fluorouracil (MF protocol) or tegafur (F protocol). A total of 514 cases with inoperable or recurrent gastric cancer were randomly allocated to either the SPG group or the control group, 367 of which were finally assessed for clinical efficacy. SPG was intramuscularly given at a dose of 20 mg twice a week or 40 mg once a week. Significant prolongation of life span was confirmed in the SPG group (MF protocol: p less than 0.01, F protocol: p less than 0.05), although the combination of SPG did not demonstrate a remarkable antitumor effect in both MF and F protocols. Among immune response parameters tested, the positive reactions in the PHA skin test were maintained in the SPG group and decreases in lymphocyte counts were inhibited by SPG in the MF protocol. Side effects associated with SPG therapy were noted in 6 of 258 cases treated with SPG. From these results, it is indicated that the combination of SPG and the chemotherapeutic agents may be useful in treating patients with inoperable or recurrent gastric cancer.