Out of 642 primary lung cancer patients who underwent surgery between 1986 and 1992, 82 cases who underwent curative resection were enrolled for a randomized prospective controlled study of postsurgical adjuvant immunotherapy using Interleukin 2 (IL-2) and lymphokine activated killer (LAK) cells. From 1986 to 1989 (the initial period), Stage IIIA patients were divided into three groups: group A (chemo-immunotherapy) received IL-2, LAK cell adoptive immunotherapy after two courses of anticancer (CDDP, VDS, MMC) chemotherapy, group B (control) received no adjuvant therapy, and group C (chemotherapy) received the same anticancer chemotherapy as group A. In the latter (1990-1992) period, group C was discontinued because of poor results and Stage II and IIIA cases were randomly assigned to group A or B. The 5- and 7-year survival rates of group A (33 cases) ana B (36 cases) were 58.2% and 31.5%, respectively in Stage II and IIIA cases. The prognosis of group A was significantly better than that of group B (P = 0.0038 by the Cox-Mantel (C-M) test and 0.0033 by the generalized Wilcoxon (G-W) test). The 5- and 8-year survival rates of each group for Stage IIIA cases were 53.4% (group A, 25 cases), 33.4% (group B, 26 cases), and 30.8%, 15.3% (group C, 13 cases). The prognosis of group A was significantly better than that of group B (P = 0.045 by the C-M and 0.036 by the G-W test). The difference between group A and B was also significant in N0, N1 (P < 0.01), in T1, T2 (P < 0.01), and T3 (P < 0.05) cases. These results indicate that adjuvant immunotherapy using IL-2 and LAK cells in combination with chemotherapy is significantly effective in improving the postsurgical prognosis of lung cancer patients.