Recent technological developments have made it possible to measure intraluminal pH simultaneously at multiple sites using one single small-caliber catheter. The aim of this study was to investigate the dynamics of physiological gastroesophageal reflux in eight ambulatory healthy volunteers (age 21-51 yr). Esophageal pH was recorded for 24 h at 3, 6, 9, 12 and 15 cm from the lower esophageal sphincter (LES), using an 8-Fr catheter containing five ion-sensitive field effect transistor (ISFET) pH transducers and a digital data logger. Signals were sampled at a rate of 4 Hz. Automated analysis included determination of the extent of the reflux (cm above LES) and calculation of the velocity of the advance of the pH front from the LES (ascending velocity), minimum pH reached, and duration of all individual reflux episodes at different segments in the esophagus. The reflux time and the number of reflux episodes/24 h showed a gradual decrease from the distal to the proximal sensor (mean +/- SE: 4.4 +/- 0.8 to 0.9 +/- 0.2% and 46 +/- 7.6 to 11 +/- 1.9, respectively). Of all reflux episodes 23% did not reach the sensor at 6 cm above the LES, and only 25% reached the most proximal sensor. Characteristically, acid refluxed rapidly (velocity 0.4-2.4 cm/s) and was cleared in a stepwise fashion. Reflux episodes of long duration at the distal sensor reached high levels in the esophagus (P < 0.001). It was concluded that ambulatory multichannel esophageal pH monitoring using ISFET technology is a valuable tool for studies on the spatio-temporal characteristics of gastroesophageal reflux.