Cryonecrosis of the upper lobe of the lung and bronchi was safely inudced in healthy dogs by application of the cryoprobe to serosal surfaces or, through a bronchotomy, to the mucosal surfaces under direct vision. Seven days after cryosurgery, hyperemia of the bronchus was seen. By 14 days the bronchus at the target site was covered with cuboidal epithelium. Reappearance of normal ciliated epithelium occurred by 180 days after cryosurgery. Cartilage remained intact, and there was no evidence of formation of a stricture or other gross alteration of bronchial architecture. In the lung there was coagulation necrosis; and by 14 days after cryosurgery, there was fibrosis in the target area. There were no complications of the pleural space. Cryosurgery of tissues at the margins of the bronchotomy does not impair healing. Cryosurgery may reduce the necessity for extensive surgery in selected patients with bronchopulmonary tumors, including those inaccessible to the rigid bronchoscope. Clinically, eight patients with recurrent bronchogenic tumors have received palliation by transbronchoscopic cryosurgery.