Two hundred and nineteen patients with resected lung carcinoma were randomized 3 weeks after surgery between two treatment arms: a control group (110 cases) and an immunotherapy group (109 cases). The immunostimulant was a nonviable saprophytic mycobacterium, M. smegmatis, given monthly by subcutaneous injection in four sites. The two groups were equivalent in terms of prognostic factors, including a nonsignificant difference favoring the control group based on the N (node) classification. This interim analysis was carried out on June 1, 1981. Treatment comparison by the log-rank test did not show any significant differences between these two groups in regards to disease-free interval and overall survival. There was no significant difference between the two groups after stratification of the comparison according to the N classification or adjustment with a subset of eight prognostic parameters through the Cox model. The initially expected difference (20% 1-year survival) will probably not be achieved, given these interim results, but patients will continue to be treated and followed-up according to the protocol as to allow further evaluation of this nonspecific immunotherapy.