Airway symptoms are often caused by aspiration of refluxed materials into the larynx. In this study we sought to define the frequency, character, and proximal extent of refluxed contents - including nonacid reflux-in normal subjects using intraluminal impedance to improve our understanding of the relationship between reflux and aspiration. Ten subjects, who had no symptoms of gastroesophageal reflux disease or airway disease, underwent impedance/pH monitoring with a catheter that allowed simultaneous esophageal and pharyngeal monitoring. Impedance detected 496 gastroesophageal reflux episodes in the 10 subjects during 240 hours of study. The majority, 399 (81% of the total) were acid reflux episodes (pH < 4). Ninety-seven were nonacid (pH > 4). Most reflux episodes (348 of 496) reached the mid esophagus (9 cm above lower esophageal sphincter). There were 51 reflux episodes that reached the pharynx (PR). Only 13 (25%) of PR were acidic (pH < 4), while 38 were nonacid. Twenty-six PR episodes were liquid and 25 were mixed (liquid and gas). The median number of PR episodes measured with impedance was 5 (0-10). In asymptomatic subjects, most episodes of gastroesophageal reflux are acidic and reach the midesophagus. Reflux into the PR appears to be more common than previously believed, and most of these episodes are not acidic. Thus, traditional 24-hour pH monitoring may underestimate the presence of pharyngeal reflux. The combination of impedance with pH monitoring markedly enhances our ability to accurately detect potential microaspiration.