We evaluated the efficacy of noninvasive mechanical ventilation (NIMV) in alleviating distress and avoiding intubation in patients with de novo acute respiratory failure complicating primary medical disorders. Eleven consecutive patients with severe respiratory distress were entered. In all patients a decision to intubate on an urgent basis had been made, but NIMV could be initiated within minutes. The patients suffered from acute pulmonary edema (five), sepsis/ARDS (two), status asthmaticus (two), and severe pneumonia (two). Dyspnea score (max=10) was (+/- SD) 8.4 +.- 1.6, scale for accessory muscle use (max=5) was 4.2 +/- 0.7, and respiratory rate was 37.6 +/- 3.8 min -1. Pa CO2, pH, and base excess (BE) were 48 +/- 18 mm Hg, 7.27 +/- 0.13, and -5.5 +/- 7.4, respectively, with five patients showing severe metabolic acidosis (BE < - 10). NIMV was applied using proportional assist ventilation. There were three early failures. These included the two patients with sepsis/ARDS who did not tolerate the mask. One patient failed because Pa CO2 and pH deteriorated despite subjective improvement. The remaining eight patients demonstrated progressive improvement, and none required intubation. The duration of NIMV was 3 h to 2 d. We conclude that when NIMV is made available on a "few minutes" basis, selected patients with severe de novo respiratory distress/failure caused by reversible medical disorders, who would otherwise have been intubated, can be given substantial relief and be spared intubation.