Pulmonary edema fluid and serum samples were obtained from 20 patients with cardiac and noncardiac pulmonary edema, and total protein, albumin, and globulin concentrations were measured. The mean edema fluid to serum protein ratio in patients with pure cardiogenic pulmonary edema was 0.37 +/- 0.09. In contrast, the patients with pure noncardiogenic pulmonary edema had protein ratios of 0.84 +/- 0.12 (p less than 0.001). Another group of patients with both cardiac and noncardiac causes for edema demonstrated edema fluid to serum protein ratios that were significantly higher than those found in the cardiogenic patients and lower than the protein ratios in the noncardiogenic patients (0.60 +/- 0.07) (p less than 0.01) A cardiac or noncardiac causes of pulmonary edema could be determined in all patients, using edema fluid to serum total protein ratios in conjunction with globulin ratios. Cardiogenic and noncardiogenic pulmonary edema represent the extremes in the spectrum of pulmonary edema. A combination of increased permeability and hydrostatic pressure may account for an intermediate form of pulmonary edema.