Twenty patients (ten with mitral and/or aortic valve disease and ten with ischemic heart disease, all in the New York Heart Association class IV, aged between 18 and 74 yr, with cardiogenic pulmonary edema unresponsive to drug treatment) were treated with polysulphone membrane ultrafiltration (UF) in a veno-venous circuit. All patients had dyspnea, pulmonary rales, hypoxemia, tachycardia, hypotension, overhydration, radiologic evidence of engorged pulmonary vasculature, and Kerley-B lines. Systemic and pulmonary arterial pressures, cardiac output (by thermodilution), and intrapulmonary shunt fraction (Qsp/Qt) were determined and chest x-ray was obtained at the beginning and the end of UF. Average duration of the treatment was 150 +/- 28 min; UF volume averaged 3000 +/- 170 ml. UF reduced the Qsp/Qt by 58% from control condition, and did not significantly affect hemodynamic variables. Chest x-rays documented clearing of alveolar edema and venous congestion. These changes were associated with unequivocal clinical improvement and no mechanical ventilation was necessary to improve gas exchange. Short-term fluid subtraction did not result in undesired circulatory alternations. Because the ultrafiltrate composition is similar to plasmatic fluid, no modification in the plasma osmolarity was detected. In conclusion, UF may be considered an effective tool for the treatment of acute pulmonary edema refractory to drug therapy, as an alternative to mechanical ventilation, and as a remedy for excessive extravascular lung water.