Fifty-two stage I and II patients with nonsmall cell lung cancer were randomized after resection to no further therapy, BCG, or BCG plus allogeneic tumor cells. Patients have been observed for 16-65 months (mean 39.5). When the two immunotherapy arms were combined and plotted against controls, trend analysis suggested (P = 0.088) an increase in disease-free interval (DFI) only for stage I patients. The one-way mixed lymphocyte culture (MLC) values were depressed in some patients prior to any immune stimulation. Immunotherapy significantly benefited DFI among patients with a depressed MLC.