Esophageal acid sensitivity was evaluated in 15 patients with Barrett's esophagus and in 15 patients with reflux esophagitis uncomplicated by Barrett's. Patients with Barrett's esophagus had sensitivity to esophageal acid perfusion less frequently than those with uncomplicated reflux esophagitis (66 vs. 100%; p < 0.05). Moreover, patients with Barrett's esophagus with acid sensitivity took longer to develop pain during acid perfusion (p < 0.05), and overall, experienced less severe symptoms (p < 0.01) than those with reflux esophagitis. Over a 2-week period, as judged by diary, the Barrett's group had less frequent (p < 0.01) and less severe (p < 0.01) heartburn symptoms than the other patients. These results indicate that patients with Barrett's esophagus have significantly reduced esophageal acid sensitivity and, as a consequence, have an impaired ability to recognize acid reflux.