The response of lung to nonpenetrating blunt trauma of the magnitude that is often found in automotive accidents or falls has not been extensively studied. An evaluation and correlation of roentgenographic and clinical findings in 20 patients with traumatic nonpenetrating contusion of the lung form the basis of this report. In no case was there loss of skin integrity or rib fracture. The characteristic radiographic patterns and rate of resolution of the lung lesions are documented. Possible mechanisms of injury are discussed. Representative pathologic changes in three cases that came to autopsy are compared with the roentgenograms. Mechanisms of Injury The mechanisms of blast injury were investigated by Zuckerman (10) in 1941. In man, the positive pressure component of the blast wave acts as a direct force on the thoracic cage and causes injury to the underlying lung. These blast injuries vary clinically from cough in cases of lesser severity (2) to hemoptysis, chest pain, shock, and prostration (5). The ...