Experiments were carried out on 30 dogs to investigate the course of respiration during obstructive asphyxia. They were asphyxiated by occlusion of the exposed trachea. Intrathoracic pressure, blood pressure in the femoral artery, electrocardiogram and electroencephalogram readings were registered. In most cases, the respiration course during the dyspnea stage by occlusion of the trachea generally had an inspiratory character. In a few animals, when the trachea was occluded in the expiratory phase, there were a few positive expiratory respirations with moderate inspiratory movement and thereafter the respirations were inspiratory during the dyspnea stage. The terminal respirations, which occurred 1-2 min before the circulatory breakdown, were generally inspiratory, but in a few dogs they were expiratory.