Thirty infants less than 12 mo old (19 with pathologic gastroesophageal reflux and 11 symptomatic controls) underwent continuous monitoring of distal esophageal pH with simultaneous pharyngeal and multiple-site esophageal manometry to compare acid clearance times of awake and asleep reflux episodes. While awake, acid clearance times of the two groups were equivalent. While asleep, mean acid clearance time increased in subjects with pathologic reflux greater than 500% while remaining essentially unchanged in symptomatic controls. No difference in minimum pH attained during sleep reflux, in percentage of swallows resulting in esophageal peristalsis, or in the frequency of secondary peristaltic waves was found to explain the difference in sleeping acid clearance times in the two groups. However, there was a significant difference between the groups with respect to swallowing rate (p less than 0.01). During sleeping reflux episodes, subjects with pathologic reflux swallowed 0.5 +/- 0.1 times per minute (mean +/- SEM), whereas controls who refluxed swallowed 3.5 +/- 1.3 times per minute. During awake reflux episodes the swallowing rates were equivalent in the two groups, 4.1 +/- 0.4 and 4.7 +/- 0.7 per minute, respectively. We conclude that low swallowing rate during sleeping reflux episodes is primary to the delayed clearance of sleeping reflux in these infants.