Systemic air embolism following penetrating injuries of the lung has not been widely recognized clinically. Experimental studies designed to reproduce the phenomenon in dogs have been at variance, although none has taken into consideration the often high intrabronchial pressures created during resuscitative efforts in such patients. Twelve patients with systemic air embolism following penetrating traumatic injuries to the lung have been seen at our hospital. Ventilatory pressures created during resuscitative thoracotomy in traumatized patients were monitored and found to be as high as 100 mm Hg. Penetrating injuries of the lung were created in mongrel dogs, and the animals were ventilated with pressures reaching 90 mm Hg. All dogs unequivocally developed systemic air embolism, with air visualized in the coronary arteries. It would appear that systemic air embolism following penetrating injury to the lung may result when increased intrabronchial pressure, such as found during manual ventilatory assistance, forces air through traumatic bronchovenous fistulae into the systemic circulation.