A randomized clinical trial of intrapleural Nocardia rubra cell-wall skeleton (N-CWS) followed by intradermal N-CWS was performed against lung cancer patients from November, 1977 to June 1981. Totally, 190 patients were entered into this trial. The N-CWS treatment was effective in terms of prolongation of remission duration against not only operable but also inoperable patients. However, significant improvement of survival rate was observed only in operable patients, especially curative+relatively curative resection-group (p less than 0.05). The mode of recurrence was classified as local recurrence and distant metastasis in the curative+relatively curative resection-group. The rates of distant metastasis were 34.1 and 17.6%, respectively, in the control and the N-CWS groups. The rate of local recurrence was 13.6% in the control group, however, no local recurrence was observed in the C-NWS group. These results indicate the clinical effectiveness of the N-CWS treatment especially in curatively resectable lung cancer. No serious side effect was experienced during this trial.