Strapless oral-nasal interface for positive-pressure ventilation. A custom-fabricated strapless oral-nasal interface (SONI) is described. It was used in the long-term administration of intermittent positive-pressure ventilation (IPPV) by 18 patients with paralytic or restrictive pulmonary insufficiency. This interface is an acrylic shell which is firmly fixed to an orthodontic bite plate; it is designed to form a seal over the nose and mouth for the entry of IPPV. Eight patients were ventilator dependent 24 hours a day. The ten patients who required only nocturnal aid had improvement in daytime arterial blood gases. Although nine of these patients could manage less than 15 minutes of unassisted breathing (free time) supine, all slept supine on SONI IPPV. The 13 patients who underwent sleep monitoring maintained a mean oxygen saturation of 95.3% +/- 1.7% and acceptable end-tidal pCO2 (30 to 45 mmHg). These 13 patients have used SONI IPPV for an average of 22 months (range = 3 to 63 months). Impediments to successful long-term use of a SONI include the presence of a hyperactive gag reflex or stimulation of excessive oral secretions. When combined with mouth IPPV, glossopharyngeal breathing, the intermittent abdominal pressure ventilator, or the cuirass ventilator for daytime use, SONI IPPV is an option for the patient who prefers total ventilatory support by noninvasive means. 