To study the relationship between sedation and respiration under N2O, we performed polysomnographic recordings in 15 healthy men with documented normal breathing patterns during sleep. In a first study in five subjects, we found that 50% N2O in O2 compared to 50% O2 increased sleep latency to stage 2 (59 +/- 12 vs. 17 +/- 3 min), total sleep duration (59 +/- 12 vs. 26 +/- 11 min), depth of sleep and respiratory events during sleep (18 +/- 5 vs. 1 +/- 1/h of sleep). In a second study, ten subjects were exposed to N2O (30 and 50%) in O2 during two consecutive experimental periods. Eight subjects had EEG features of physiological sleep, but nevertheless exhibited a total of 181 respiratory events. Respiratory disturbance index (RDI) during sleep was similar under 30 and 50% N2O (25 +/- 7 and 25 +/- 5/h of sleep, respectively). Obstructive events predominated, except in three subjects during N2O 30% and one during N2O 50% exposure. We conclude that N2O can induce central and obstructive sleep apneas.