(1) By investigating many autopsy cases, it was found that the incidence of combination of the pulmonary edema was high in the cases with central nervous system diseases, particularly in the cases having localized foci in the vicinity of the internal capsule, the lentiform nucleus and the third ventricle. (2) From the histological viewpoint, an attempt was made to classify the clinical cases of postoperative acute pulmonary edema into 3 groups: (1) that occurring after a brain operation or brain trauma, (2) that occurring after a cardiopulmonary operation of cases with pulmonary circulatory disturbances, (3) that occurring after an abdominal operation of cases with metabolic disorders. It is worthy of note that the incidence of the postoperative pulmonary edema was significantly high after brain surgery. (3) In the examination of the pulmonary vascular innervation, the reflex pathway has been clarified and the 2 centers were assumed to be in the reflex arc of the innervation of the pulmonary vessels. The higher center of the reflex arc ascending through the vagus nerve was in the nuclei of the preoptic areas, while the lower center of the reflex arc ascending through the sympathetic or sinus nerve was in the medulla. The authors have also confirmed that the site of cerebral damage in the clinical cases of pulmonary edema, occurring after a brain operation or a brain trauma, had a close relation to either the higher or the lower center of the pulmonary vascular innervation or the both. (4) The authors have succeeded in the experimental production of the characteristic pulmonary edema of cerebral origin by a complete destruction of the bilateral preoptic areas. Pathophysiology concerning the experimentally produced pulmonary edema has been studied in detail. (5) Based on the results of both clinical and experimental studies, the pathogenesis of the clinical pulmonary edema occurring after a brain operation or a brain trauma was assumed to be as follows. The operation or trauma was directly responsible for the development of pulmonary hypertension, the prolongation of pulmonary circulation time, and the increase in the permeability of the pulmonary capillaries. At the same time, the operation or the trauma directly caused the changes in renal or hepatic circulation and endocrine regulation, inducing anuria, disturbance of water and electrolytes balances. The combination of these factors accelerated a selective pulmonary edema of an acute type.