Abstract. Objective: To evaluate the utility of bilevel positive airway pressure (BiPAP) in the out-of-hospital treatment of patients with presumed congestive heart failure (CHF). Methods: This was a prospective, sequential, parallel trial in an urban setting served by a single emergency medical services (EMS) system between January 4 and April 15, 1999. A convenience sampling of adults who were transported by rescue units judged to be in CHF by treating emergency medical technicians trained in advanced life support (ALS EMTs) was included. Rescue squads were divided into demographically matched pairs, and one of each was equipped with a BiPAP ventilatory support unit. Bilevel positive airway pressure therapy was added to the existing treatment protocols for eligible study patients. Main outcome measures were out-of-hospital treatment time, oxygen saturation changes, hospitalization length, need for endotracheal intubation, mortality rate, and ease of use of the device by EMS personnel. Results: Sixty-two of 71 enrolled patients completed the study. Out-of-hospital treatment times did not differ between groups (31.2 minutes vs 31.4 minutes; p = 0.931). The difference between pre- and post-treatment oxygen saturation levels was greater for the BiPAP group (13.71%) than the control group (6.69%) (p < 0.05). There was no statistical difference between groups in the length of hospital stay [control: 7.63 days, vs BiPAP: 6.33 days, p = 0.48], the intubation rate [control: 7 of 25 (28%) vs BiPAP: 4 of 37 (11%), p = 0.10], or death rate [control: 2 of 24, vs BiPAP: 6 of 37, p = 0.46]. All of the ALS EMTs who used BiPAP thought that it was safe to use, and 97% thought it was easy and appeared to improve patients' dyspnea and respiratory distress. Conclusions: ALS EMTs can be trained to deliver noninvasive ventilation with BiPAP, find it easy to apply, and believe that it helps relieve dyspnea in patients with suspected CHF.