Intrapleural Corynebacterium parvum 7 mg or placebo was administered postoperatively as adjuvant therapy to patients with resected Stage I and II non-small cell lung cancer in a prospective, randomized, multicenter trial. A total of 475 patients were entered into this study between July, 1977, and February, 1979. Of this group, 405 can be evaluated, with an average follow-up time of 4.6 years. More side effects, especially fever and chest pain, were observed in patients receiving Corynebacterium parvum (p less than 0.001). An increase in fever was associated with a decrease in survival (p = 0.01). Life-threatening or fatal complications were not seen. Important prognostic factors are surgical stage (p less than 0.001) and degree of differentiation (p = 0.02). Corynebacterium parvum is associated with a decreased survival (p = 0.02). It is concluded that intrapleural Corynebacterium parvum is detrimental to survival.