To identify tracheobronchial abnormalities associated with assisted ventilation, 40 infants with respiratory distress syndrome randomized to receive either short-term (48 hours) conventional or high-frequency jet ventilation were studied. Flexible fiberoptic and bronchoscopy (n = 13) was performed and/or clinical and radiographic assessments were used to evaluate for laryngeal, tracheal, and bronchial lesions. There was no bronchoscopic evidence of necrotizing tracheobronchitis after either high-frequency jet ventilation (n = 8) or conventional ventilation (n = 5). Laryngotracheomalacia and nodular vocal cords were the most common abnormalities noted, and they occurred with equal frequency in both groups. Study infants who were not bronchoscoped had no clinical or radiographic evidence of tracheal or mainstem bronchial obstruction. One patient did have microscopic evidence of necrotizing tracheobronchitis at autopsy, however. It is concluded that short-term treatment of respiratory distress syndrome with high-frequency jet ventilation may be performed without undue risk of tracheobronchial injury.