1. Lateral roentgenograms demonstrate that the edema which appears central on the frontal roentgenogram may, in fact, lie in anterior or posterior segments of any lobe of the lung. 2. Interstitial and intra-alveolar pulmonary edema accompany each other in most patients irrespective of the cause. 3. There are specific signs of interstitial edema, such as septal lines and peribronchial and perivascular cuffing. but others, such as perihilar haze, can be confused with intra-alveolar edema. 4. Although gravity probably plays a part in the distribution of edema, it is difficult to obtain conclusive evidene of this in all cases. 5. Pulmonary edema appears to shift easily and rapidly from lobe to lobe and from one lung to the other.