Animal experiments were performed with evaluation of the use of the neodymium-YAG (yttrium-aluminum-garnet) laser in the trachea, bronchi, and pulmonary parenchyma. Histologic evaluation of incisions into the lung was assessed by multiple sections over a 5-week period and comparisons were made of incisions closed with chronic catgut or coagulated with electric cautery or by the laser. These studies indicated that the laser is more effective in controlling parenchymal bleeding and air leaks than either the cautery or chromic catgut and produces less local tissue reaction. The Nd-YAG laser has been used clinically to treat patients with inoperable obstructing and bleeding carcinomas of the trachea and main bronchi to open the involved airway and to restore pulmonary function. Fifteen patients have had 26 treatments using the Nd-YAG laser. Total laser time was limited to 15 minutes with 0.5-second pulses of 50 to 80 watts being delivered via the fiberoptic and straight bronchoscope as indicated. It is extremely effective in controlling hemoptysis from recurrent endobronchial lesions, and obstructing lesions in the trachea and main stem bronchus can be treated quite successfully with excellent palliation. It is apparent that continued clinical use of the Nd-YAG laser as palliative therapy for bleeding and obstructing tumors of the tracheobronchial tree is indicated and expanded use at the time of thoracotomy to control lung parenchymal bleeding and air leaks should be considered in the future.