Barrett's esophagus is a metaplastic condition associated with gastroesophageal reflux disease and an increased risk for adenocarcinoma. Acid plays a significant role in the development and progression of Barrett's esophagus and high dose proton pump inhibitor (PPI) therapy is often needed. The aim of this study is to assess the efficacy of esomeprazole, a new potent PPI, on symptom relief and intraesophageal and intragastric acid suppression in patients with Barrett's esophagus (BE). Patients were evaluated by standardized questionnaires and dual sensor 24-h pH monitoring while receiving esomeprazole at a dose (40-80 mg/day) needed for control of symptoms. Analyses of intraesophageal and intragastric pH profiles were then made. Thirteen patients, mostly men, were studied. All tolerated esomeprazole (40-80 mg/day) with good symptom control. Sixty-two percent of patients with BE had abnormal intraesophageal pH profiles despite adequate symptom control on esomeprazole which was associated with significant breakthrough of intraesophageal acid control, particularly at night. Low nocturnal intragastric pH correlated highly with nocturnal intraesophageal acid reflux (P = 0.004) and there was a relative failure of nocturnal intragastric acid control with esomeprazole. A high percentage of patients with BE continue to exhibit pathologic GERD and low intragastric pH despite esomeprazole for reflux symptom control. For an antisecretory treatment aimed at chemoprevention of esophageal adenocarcinoma to be effective, higher PPI dosing confirmed by pH monitoring may be necessary.