A randomly controlled study of chemotherapy versus chemoimmunotherapy was performed in patients with operable lung cancer from November 1977 to June 1981. The immunotherapy consisted of an intrapleural instillation of Nocardia rubra cell wall skeleton (N-CWS) followed by serial intradermal N-CWS. A total of 119 patients were entered into this trial. There were 64 evaluable patients in the control group and 52 evaluable patients in the N-CWS group. N-CWS treatment was effective in terms of prolongation of duration of remission for all operable patients. Although significant improvement in the survival rate was not observed in patients at Stages I and II (p less than 0.10), it was observed in the curative operation group (p less than 0.05). The mode of recurrence was classified as local recurrence and distant metastasis in the curative operation group. The rates of distant metastasis were 34.0 and 18.9%, respectively, in the control and the N-CWS groups. The rate of local recurrence was 14.9% in the control group; however, no local recurrence was observed in the N-CWS group. These results indicate the clinical effectiveness of the N-CWS treatment, especially in curatively resectable lung cancer. No serious side effect was observed during this trial.