Postoperative immunochemotherapy with mitomycin C (MMC), 5-fluorouracil (5-FU) and OK-432 was evaluated as adjuvant therapy for curative resection in the cases of gastric cancer. One hundred and twenty-two patients (28 were excluded) were randomly assigned to 3 groups: Group A-MMC and 5-FU (28 cases); Group B-MMC, 5-FU and OK-432 (33 cases); Group C-control (33 cases). There were no differences in the back ground factors influencing survival time among each group. Group B showed better results in survival rate and disease free interval as compared with Group A or C. Minor and reversible side effects such as enterogastric disorder, leukopenia (less than 3000/mm3), thrombo cytopenia (less than 7 X 10(4)/mm3) and elevation of serum transaminase (S-GPT greater than or equal to 100 unit) were equivalently observed in frequency in each Group A and B, but they were milder in Group B than Group A.