Acute pulmonary edema was induced in anesthetized vertically suspended dogs by inflating a ballon catheter in the descending thoracic aorta and infusing saline. Indices measured included pulmonary arterial pressure, left ventricle end-diastolic pressure, and cardiac output. Pulmonary blood-flow distribution was determined in frozen tissue after injecting radioactive macroaggregates labelled with 125-I, 131-I, and 99m-Tc. Randomized serial chest roentgenograms were interpreted by three radiologists not taking part in the physiologic studies. When left ventricular end-diastolic pressure was raised initially, roentgenograms usually revealed only interstitial edema. As alveolar edema increased, blood-flow to the lung bases decreased as measured physiologically. The roentgenographic and physiologic data show that in acute experiments on normal lungs, blood-flow redistribution occurs in association with alveolar edema rather than interstitial edema.