The aim of this study was to assess the quantitative differences of acid exposure at 1 cm and 6 cm above the squamocolumnar junction (SCJ) using two radiotelemetry pH capsules affixed to the esophageal mucosa. Ten normal subjects and 10 endoscopy-negative gastroesophageal reflux disease (GERD) patients without hiatus hernia (ages 20-54, 12 male) were studied for a 24-h period using the Bravo pH monitoring system. pH capsules were placed 1 cm and 6 cm above the SCJ. Interpretable data for at least 14 h was obtained in 18 of the 20 subjects (9 normal, 9 GERD). Two failures occurred secondary to early capsule dislodgement. Median esophageal acid exposure was significantly increased at 1 cm above the SCJ compared to 6 cm above the SCJ during the total, upright and postprandial time periods in both normal and GERD subjects. During a 2 h postprandial period the esophageal acid exposure was 8-fold greater in GERD subjects and 5-fold greater in normal subjects 1 cm above the SCJ compared to 6 cm above the SCJ. Confident measurement of esophageal acid exposure at a fixed position 1 cm above the SCJ is feasible with the Bravo system. Acid exposure was significantly higher 1 cm above the SCJ compared to 6 cm above the SCJ in both GERD patients and controls. These findings suggest that measurement of acid exposure 1 cm above the SCJ may improve accuracy of pH monitoring by detecting acid reflux events confined to the distal esophagus.