Abstract Ultrafiltration, the process by which plasma water is removed from the blood was utilized to determine its effect on lowering lung water in pulmonary edema produced by fluid overload, steam inhalation, and endotoxin. Lung water was measured by the thermal-dye indicator dilution technique which correlated well with lung water measured gravimetrically over a wide range ( r = 0.95). Edema was produced by fluid overload in five mongrel dogs (Group I), by steam inhalation (Group II), and by endotoxin (Group III). Extravascular lung water (EVLW) rose significantly ( P = <0.05) from control levels with the production of the edematous states (Group I: 8.0 ml/kg (mean) ± 1.9 (SD) to 13.1 ± 1.9); (Group II: 8.1 ± 1.0 to 10.7 ± 0.7); (Group III: 7.4 ± 0.9 to 10.3 ± 1.2). EVLW then fell significantly ( P = <0.05) after ultrafiltration in all three groups (Group I: 8.9 ± 2.4; Group II: 7.8 ± 1.9; Group III: 7.7 ± 1.4). Ultrafiltration was effective in reversing pulmonary edema and may have clinical application when excess lung water interferes with cardiac or pulmonary function.