Recent studies have shown that impaired esophageal clearance of refluxed material during the sleeping interval plays a major role in the pathogenesis of esophagitis. The present investigation compares esophageal responses to both acid and water infusions during sleep in asymptomatic subjects. Fourteen healthy individuals were studied. The subjects were studied for two nights in the sleep laboratory. Each night involved four to six infusions of 15 ml of either sterile water or 0.1 N HCl. A similar infusion was conducted during the presleep waking interval. Acid clearance time was shown to decrease as a function of increasing wakefulness during the acid clearing interval. Arousal responses were significantly greater with acid infusions during sleep (p less than 0.05). Awakenings from sleep with acid infusions were associated with significantly greater swallowing rates than those associated with water infusions (p less than 0.01). Peristaltic parameters of amplitude, velocity, and duration were not differentially affected by acid versus water infusions or by sleep versus waking.