A clinical trial has been established to evaluate the use of intralesional bacillus Calmette Guérin (BCG) immunotherapy as an adjunct to surgery in resectable pulmonary neoplasms. BCG was injected percutaneously under fluoroscopic guidance into a single nodule in each of 21 patients with resectable primary and metastatic pulmonary neoplasms. Eighteen of 21 infected nodules increased in size and nine became poorly defined in the 2-4 week interval between BCG administration and resection. There was no change in those nodules that were not injected. The changes in the injected nodules were due to BCG-induced granulomatous inflammation and necrosis. BCG can be administered intralesionally into pulmonary neoplasms without significant complications (pneumothorax in nine, intrapleural injection in one). Preliminary observations suggest an improvement in disease-free interval. A prospective, randomized trial is planned to determine whether BCG immunotherapy will result in significantly improved survival in patients with primary and metastatic pulmonary neoplasms.