We assessed the effect of 30 mg of oral flurazepam on sleep-disordered breathing and nocturnal oxygen desaturation by performing a double-blind, placebo-controlled, randomized study. Asymptomatic subjects, 17 men and three women (mean age 49 years, mean weight 79 kg), were monitored for two consecutive nights. Flurazepam was given to 10 subjects on night 1 and to 10 subjects on night 2. Placebo was ingested on the other nights. Polysomnographic determinations included chest wall movement by impedance pneumography, nasal and oral airflow by thermistor probes, and continuous oxygen saturation by ear oximetry. Flurazepam was associated with significant increases in the number of sleep events (p = 0.01), episodes of apnea (p less than 0.01), and total duration of apnea (p less than 0.01). The number of episodes of hypopnea of desaturation did not significantly increase, although the degree of desaturation increased after flurazepam ingestion (p = 0.04). Total sleep time significantly increased (p = 0.04), but could not account for the increased number of events. Sleep stage distribution was minimally altered by ingestion of flurazepam.