Nasal respiratory airflow resistances of awake snorers averaged 0.188 +/- 0.165 Pa/cm3/s (N = 306) and were not elevated beyond the normal range (less than 0.25 Pa/cm3/s). Resistances were decreased substantially from a mean of 0.164 +/- 0.128 to 0.065 +/- 0.037 Pa/cm3/s (N = 72) by a nasal vestibular dilator (Nozovent). Effects of the dilator on breathing disorders in sleep were determined by polysomnographic recordings that included frequency, duration and intensity of snoring, apneas, hypopneas, and oxygen saturation in 10 heavy snorers while asleep with and without the dilator in situ over periods of several hours. No significant changes were detected in these parameters in any stage of sleep.