To determine the group of patients for whom a biological response modifier is useful, the efficacy of postoperative adjuvant immunotherapy was investigated with regard to infiltration of dendritic cells (DC) in patients with advanced gastric cancer who underwent absolute curative resection. The infiltration of DC was classified into marked and slight. The chemotherapy group was prescribed mitomycin C and tegafur, while for the immunochemotherapy group a biological response modifier, PSK, was also prescribed in survival between the chemotherapy and immunochemotherapy groups. In patients with slight infiltration, however, the 5 - year survival rates were 0% in the chemotherapy and 15% in the immunochemotherapy group. Patients given PSK survived longer than those given chemotherapy only (P less than 0.05). Therefore, adjuvant immunotherapy may be considered for patients with advanced gastric cancer with slight infiltration of DC.