Gastroesophageal reflux and esophageal motility were studied for 24 hr in 32 ambulatory healthy volunteers (20-73 years old), using a newly developed system, consisting of a microprocessor-based data recorder and algorithms for fully automated data analysis. Physiological reflux was more extensive than expected on the basis of widely used normal values. The percentage of time with pH less than 4 and the duration of the reflux episodes increased with age. Of the more than 2000 esophageal contractions occurring per day, peristaltic contractions constituted 50.9 +/- 2.0%. Their amplitude was significantly lower between meals than during meals and during the night. The duration of the peristaltic contractions increased with age. Simultaneous contractions constituted 10.4 +/- 1.2% of the esophageal contractions. Their incidence increased with age. We conclude that continuous ambulatory 24-hr recording with automated analysis of esophageal motility and pH profile is feasible, that the upper limits of normal in ambulatory esophageal pH recording are higher than previously accepted, and that age, meals, and body position must be taken into account in the interpretation of both 24-hr esophageal pH and pressure data.