The possible role of high nasal airway resistance in the pathogenesis of obstructive sleep apnea has been examined in 7 patients with seasonal (ragweed) allergic rhinitis, a naturally occurring model of reversible nasal obstruction. Measurements of nasal resistance and overnight polysomnographic studies were performed during the ragweed season when the patients complained of nasal obstruction; and 6 to 8 wk later when the symptoms had subsided (control study). During the symptomatic phase, mean (+/- SE) nasal resistance was 4.9 +/- 0.8 cm H2O/L/s, and the patients experienced 1.7 +/- 0.3 obstructive apneas per hour of sleep. In contrast, at the time of the control study, nasal resistance had decreased to 2.5 +/- 0.3 cm H2O/L/s (p less than 0.01); and the rate of obstructive apneas had decreased to 0.7 +/- 0.4 per hour of sleep (p less than 0.005). The duration of these apneas had also decreased from 15.5 +/- 0.8 s to 6.1 +/- 2.9 s (p less than 0.01). Apneas were rarely associated with significant O2 desaturation and were fewer in number than typically seen in a clinically significant sleep apnea syndrome. In male patients there was a direct relationship (r = 0.9) between the change in nasal resistance from symptomatic to control studies and the corresponding change in frequency of obstructive sleep apneas. Coincident with these respiratory changes at the time of the control study was an increase in the amount of slow-wave sleep (p = 0.05) and a small reduction in the frequency of arousals during sleep (p = NS). We conclude that in patients with allergic rhinitis, obstructive sleep apneas are longer and more frequent during a period of symptomatic nasal obstruction than when symptoms are absent. The results support the concept that a high nasal resistance may be a contributing factor in the pathogenesis of obstructive sleep apneas in general.