The mechanism for the association between gastroesophageal reflux and bronchospasm is probably multifactorial. Our data support the view that microaspiration into the trachea may be an important mechanism for bronchospasm induced by gastroesophageal reflux and needs to be distinguished from simple reflux into the esophagus. Intraesophageal acidification alone quantitatively produces a much smaller airway response than does intratracheal acidification. A challenge test should be developed to correlate airway response following intraesophageal acidification to airway hyperactivity. We believe that the relationship of the diaphragm to the antireflux barrier deserves further study.