To evaluate radiographic criteria recently proposed for determining causes of pulmonary edema, the authors studied 45 patients with severe pulmonary edema. Hydrostatic and increased permeability edemas were distinguished by means of the ratio of pulmonary edema fluid protein to plasma protein concentration and clinical and hemodynamic data. Chest radiographs were classified as showing hydrostatic, increased permeability, or mixed edema by three independent readers without knowledge of the clinical diagnosis. Overall, 87% of patients with hydrostatic edema but only 60% of patients with increased permeability edema were correctly identified. A patchy, peripheral distribution of edema was the single most discriminating criterion and was relatively specific for increased permeability edema, occurring in 13% of patients with hydrostatic and 50% with increased permeability edema (P less than .05). Some features considered more typical of hydrostatic edema were commonly found in patients with increased permeability, including a widened vascular pedicle (56%), pleural effusions (36%), peribronchial cuffs (72%), and septal lines (40%). The authors conclude that chest radiography is limited in the differentiation of type of pulmonary edema in severe cases.