Background: Patients with respiratory and laryngeal symptoms are commonly referred for evaluation of reflux disease as a potential cause. Dual-probe pH monitoring is often performed, although data on normal acid exposure in the proximal esophagus are limited because of the small number of normal subjects and inconsistent placement of the proximal pH sensor in relation to the upper esophageal sphincter. We measured proximal esophageal acid exposure using dual-probe pH and calculated a composite pH score in a large number of asymptomatic volunteers to better define normal values. Study Design: Eighty-one normal subjects free of reflux, laryngeal, or respiratory symptoms were recruited. All had video esophagraphy to exclude hiatal hernia. Esophageal pH monitoring was performed using 1 of 3 different dual-probe catheters with sensors spaced 10, 15, or 18 cm apart. The standard components of esophageal acid exposure were measured, excluding meal periods. A composite pH score for the proximal esophagus was calculated using these components. Results: The final study population consisted of 59 (49% male) subjects, with a median age of 27 years. All had normal distal esophageal acid exposure and no hiatal hernia. The 95th percentile values for the percent time the pH was < 4 for the total, upright, and supine periods were 0.9%, 1.2%, and 0.4%, respectively. The 95th percentile for the number of reflux episodes was 24 and for the calculated proximal esophageal composite pH score was 16.4. Conclusions: In a large population of normal subjects, we have defined the normal values and calculated a composite pH score for proximal esophageal acid exposure. The total percent time pH < 4 was similar to previously published normal values, but the number of reflux episodes was greater.