With a few simple modifications, an aerosol mask was adapted to deliver high concentrations of oxygen. We compared the delivery of high concentrations of oxygen by this modified aerosol mask (MAM) with that of a nonrebreathing mask (NRM) in five normal volunteers and six patients with respiratory failure. Besides improved oxygenation, the MAM also permitted the following: humidification of the inspired oxygen, nebulization of bronchodilators, oropharyngeal suctioning, and performance of fiberoptic bronchoscopy. In lieu of intubation and mechanical ventilation, MAM may be a better alternative to a NRM for maintaining adequate oxygenation until the clinical situation improves.