Results of 6589 gastric cancer operations at the Department of Surgery, Seoul National University Hospital, from 1970 to 1990 were reported. About two thirds (76.6%) were advanced gastric cancer (stages III and IV). The 5-year survival rate of operated stage III gastric cancer was only 30.6%, with frequent recurrence. Conversely, cell-mediated immunities of advanced gastric cancer patients were significantly decreased. Therefore, to improve the cure rate and to prevent or delay recurrence, curative surgery with confirmation of free resection margins and systematic lymph node dissection of perigastric vessels were performed and followed by early postoperative immunotherapy and chemotherapy (immunochemosurgery) in stage III patients. To evaluate the effect of immunochemosurgery, two randomized trials were studied in 1976 and 1981. In first trial, 5-fluorouracil, mitomycin C, and cytosine arabinoside for chemotherapy and OK 432 for immunotherapy were used. The 5-year survival rates for surgery alone (n = 64) and immunochemosurgery (n = 73) were 23.4% and 44.6%, respectively, a significant difference. In the second trial, there were three groups: group I, immunochemosurgery (n = 159); group II, surgery and chemotherapy (n = 77); and group III, surgery alone (n = 94). 5-Fluorouracil and mitomycin C for chemotherapy and OK-432 for immunotherapy were administered for 2 years. The 5-year survival rate of group I was 45.3%, significantly higher than the 29.8% of group II and than the 24.4% of group III. The postoperative 1-chloro-2.4-dinitrobenzene test, T-lymphocyte percentage, phytohemagglutinin- and con-A-stimulated lymphoblastogenesis and the antibody-dependent cell-mediated cytotoxicity test showed more favorable values in the immunochemosurgery group. Therefore, immunochemosurgery is the best multimodality treatment for advanced gastric cancer.