Pulmonary edema fluid analyses and hemodynamic evaluations were performed in two uremic patients with acute pulmonary edema. The colloid osmotic pressure of the pulmonary edema fluid ranged from 57 per cent to 93 per cent that of the serum. Although cardiac function was normal in both patients, the serum colloid osmotic pressure--pulmonary artery wedge pressure gradients were markedly reduced. Uremic pulmonary edema is the result of alterations of pulmonary intravascular Starling forces and increases in pulmonary capillary membrane permeability, allowing for the efflux of protein-rich fluid from the capillaries into the lung.