Hemodynamic evaluation in two patients and analysis of pulmonary edema fluid in one patient with diabetic ketoacidosis and acute pulmonary edema were performed. Pulmonary arterial wedge pressures in both patients were low or normal (1 and 9 mm Hg). In one patient the colloid osmotic pressure of the pulmonary edema fluid was 68 percent of the value of the serum. The serum colloid osmotic pressure-pulmonary arterial wedge pressure gradient in the second patient was markedly reduced. Pulmonary edema complicating diabetic ketoacidosis may be the result of increased permeability of pulmonary capillary membranes and altered intravascular colloid-hydrostatic forces.