Nonspecific adjuvant immunotherapy with Bacillus Calmette-Guérin cell wall skeleton (BCG-CWS) was given to 155 lung cancer patients. Clinical effects of the BCG-CWS treatment were estimated by comparing the survival of the BCG-CWS group with that of a historical control group on the basis of 4-year results. Significant prolongation of survival time has been observed in Clinical Stages II, III (M0) and III (M1). However, most Stage III patients who were given the BCG-CWS treatment died of cancer itself after marked prolongation of survival time. An increase in complete cure rate has been expected only in Stages I and II. Surgicopathological staging was used in resected cases. Resected cases at any stage were sensitive to treatment with BCG-CWS. Histologically, all types of lung cancer including squamous cell carcinoma, adenocarcinoma, and anaplastic carcinoma were sensitive to treatment with BCG-CWS. Intrapleural administration of BCG-CWS to patients with malignant pleurisy was effective in controlling the pleural effusion and prolonging the survival time. No serious complication has been experienced in our study.