Studies employing noninvasive pressure support ventilation in cardiogenic pulmonary edema have been performed in the intensive care unit when overt respiratory failure is already present and in small groups of patients. In this multicenter study, performed in emergency departments, 130 patients with acute respiratory failure were randomized to receive medical therapy plus O2 (65 patients) or noninvasive pressure support ventilation (65 patients). The primary end point was the need for intubation; secondary end points were in-hospital mortality and changes in some physiological variables. Noninvasive pressure support ventilation improved PaO2/FIO2, respiratory rate, and dyspnea significantly faster. Intubation rate, hospital mortality, and duration of hospital stay were similar in the two groups. In the subgroup of hypercapnic patients noninvasive pressure support ventilation improved PaCO2 significantly faster and reduced the intubation rate compared with medical therapy (2 of 33 versus 9 of 31; p=0.015). Adverse events, including myocardial infarction, were evenly distributed in the two groups. We conclude that during acute respiratory failure due to cardiogenic pulmonary edema the early use of noninvasive pressure support ventilation accelerates the improvement in PaO2/FIO2, PaCO2, dyspnea, and respiratory rate, but does not affect the overall clinical outcome. Noninvasive pressure support ventilation does, however, reduce the intubation rate in the subgroup of hypercapnic patients.