Gastroesophageal reflux (GERD) may trigger asthma. Approximately 77% of asthmatic people experience reflux symptoms, although GERD may be clinically silent in some. Esophagitis is found in 43% of asthmatic people, and 82% have abnormal esophageal acid contact times on esophageal pH testing. Clearly, GERD is prevalent in asthmatic people. Pathophysiologic mechanisms of acid-induced bronchoconstriction include a vagally mediated reflex and microaspiration. Whether these airway responses are clinically significant is the subject of some debate. Interestingly, peak expiratory flow rates and specific airway resistance alterations persist despite esophageal acid clearance. Preliminary evidence shows that substance P, an inflammatory mediator that causes airway edema, is released with esophageal acid. Although therapeutic studies are limited by their small population sizes and study design, up to 70% of asthmatic people have asthma improvement with antireflux therapy. Possible predictors of asthma response include patients with symptomatic esophageal regurgitation; abnormal proximal esophageal acid exposure; and, in surgical studies, those with normal esophageal motility and asthma response with medical therapy. Future research will further define the association between asthma and gastroesophageal reflux. Curr Opin Pulm Med 1999, 5:63-67.