Owing to the inherent difficulties of recording upper esophageal sphincter pressure, little is known about normal upper esophageal sphincter physiology. In this study we used a modified sleeve device to record upper esophageal sphincter pressure continuously in 8 normal volunteers. Intraesophageal pH and electroencephalogram activity were also recorded to document the occurrence of spontaneous gastroesophageal reflux and sleep. After an hour of baseline recording, the subjects ate a meal. Recording was then resumed for an additional 7 h during which period the subjects slept part of the time. The mean upper esophageal sphincter pressure was measured for each 10-min epoch. Electroencephalogram recordings were read blindly for the presence and stage of sleep. Periods of sleep were then correlated with the manometric tracings. Mean upper esophageal sphincter pressure during wakefulness, stage 1 sleep, and deeper sleep was 40 +/- 17 (SD), 20 +/- 17, and 8 +/- 3 mmHg, respectively. A significant change in upper esophageal sphincter pressure did not occur postprandially or during episodes of spontaneous gastroesophageal reflux. Upper esophageal sphincter pressure was observed to increase transiently with each inspiration during periods of restfulness and sleep, a response consistent with the hypothesis that one function of the upper esophageal sphincter is to exclude air from the esophagus during respiration. The demonstration that upper esophageal sphincter pressure falls markedly during sleep may have significance in that this diminishes the barrier to nocturnal regurgitation and potential aspiration.