Esophageal acid exposure is common in normal subjects. The aim of this study was to investigate proximal and distal esophageal acid exposure in asymptomatic volunteers using dual-channel esophageal pH-metry with probe positioning by pH step-up. A total of 21 healthy subjects (9 male; mean age, 51 years) underwent 24-hour ambulatory esophageal pH recording with the pH step-up method using a two-channel pH probe, a portable digital data recorder, and computerized data analysis. All reflux episodes, episodes longer than 5 minutes, longest reflux episode, duration of acidity (pH <4), and percentage of time with acidity were analyzed. The 95th percentile for reflux parameters assessed in the distal/proximal esophagus were: total reflux episodes, 100/34; episodes greater than 5 minutes, 2.9/0; longest reflux episode, 16.6/2.95 minutes; duration of acidity, 87.95/15.5 minutes; and percentage of time with acidity, 7.0%/1.3%. Proximal and distal acid exposure were well correlated. Results showed that neither gender nor age influenced reflux parameters and that asymptomatic volunteers might experience some gastroesophageal reflux.