Achalasia is characterized by absent orincomplete lower esophageal sphincter (LES) relaxationand aperistalsis in the smooth muscle esophageal body inresponse to swallowing. The esophageal and LES response to distention has not previously been studied.I aimed to characterize the responses to esophagealballoon distention in achalasia patients in comparisonto controls. Sixteen consecutive achalasia patients and 11 healthy volunteers underwent standardesophageal manometry followed by graded midesophagealballoon distention during which LES (as measured by theDent sleeve) and esophageal body pressures were monitored. Subject perception of distention wasalso recorded using a standardized scoring system. TheLES relaxation response to esophageal balloon distentionwas markedly impaired in achalasia patients, irrespective of whether the patient hadradiological evidence of a dilated or nondilatedesophagus. However, phasic contractions proximal to thedistending balloon were preserved. The esophageal bodyresponses below the balloon were inconsistent in bothgroups, and not significantly different from oneanother. Pain-sensation scores were significantly lowerin achalasia patients at the highest distending volumes, but this difference was attributable to thesubgroup of patients with a dilated esophagus.Distention-induced LES relaxation is markedly impairedin achalasia patients in keeping with loss of intrinsic inhibitory innervation. Preservation of theproximal excitation suggests that extrinsic vagalreflexes are intact.