The incidence of aspiration, the causative esophageal pathophysiology, and the results of surgical therapy were evaluated in 100 patients with abnormal gastroesophageal reflux documented by 24-hour esophageal pH monitoring. Based on historical evidence, 48 patients were suspected to be aspirators. Eight patients had documented episodes of aspiration (drop on esophagela pH, followed by acid taste in mouth and onset of cough or wheezing spell) during the monitoring period. Nine patients were considered to be potential aspirators because they presented oral acid regurgitation without development of pulmonary symptoms. In five patients a primary respiratory disorder (PRD) induced gastroesophageal reflux. The remaining 78 patients had abnormal reflux without aspiartion or regurgitation. Aspirators had a 75% incidence of esophageal motor abnormality on manometry, and the clearance of refluxed acid was significantly delayed in the supine position. A history of heartburn and endoscopic evidence of esophagitis were present in only half of the patients who were documented aspirators. Potential aspirators were spared from aspiration by rapid esophageal clearance of refluxed acid unaffected by changes in body position. Patients with a PRD had higher distal esophageal segment (DES) pressure and normal esophageal motility with minimal esophagitis. Nonaspirators significantly improved their clearance while in the supine position, emphasizing the protective effect of esophageal peristalsis against aspiration. An antireflux procedure in five aspirators raised the DES pressure significantly and returned the reflux status to normal by 24-hour pH-monitoring standards. The incidence of aspiration appears to be less than that suspected by history and is due to a motor disorder that interferes with the ability of the esophagus to clear reflex acid. Abnormal pulmonary symptoms can induce or result from gastroesophageal reflux and, when the latter occurs, an antireflex procedure stops both reflux and aspiration.