While nasal mucosal stimulation in animals has been reported to produce central apneas and while nasal packing in humans is known to produce sleep-disordered breathing, it is controversial whether intranasal obstruction in humans produces predominantly central or obstructive apnea. To answer this question, we studied eight normal men by having them sleep in random order with their nose open or occluded with petrolatum gauze. Esophageal pressure was measured to detect respiratory effort, and standard techniques were used to monitor and score the stages of sleep. Intranasal occlusion increased both the number of apneas plus hypopneas per hour of sleep and the minutes of obstructive events per hour of sleep (p less than 0.05). The minutes of central events per hour of sleep also increased significantly but not to the degree that occurred with obstructive events. Nasal obstruction produced no immediate changes in pulmonary function. The subject with the highest resistance measured through the mouth with the pulse flow method had the most apneas following nasal occlusion. We conclude that intranasal obstruction produces predominantly obstructive apneas and hypopneas during sleep.