This study looks the intragastric and intraesophageal pH in patients with documented Barrett's esophagus whilst taking esomeprazole 40mg twice daily, esomeprazole 40mg three times daily, esomeprazole 20 mg three times daily.

Inclusion Criteria:

• Must have a previously established, biopsy-proven diagnosis of Barrett's esophagus with segment length greater than 3cm, with no dysplasia or adenocarcinoma within the previous 12 months

Exclusion Criteria:

• A history of esophageal, gastric, or duodenal surgery, including anti-reflux surgery or endoscopic anti-reflux procedures, except for simple closure of a gastric or duodenal ulcer.
• History of various gastrointestinal diseases - please see investigator for full list.
• Evidence of any malignant disease in the last 5 years, except minor superficial skin disease.
• Unstable diabetes mellitus. Stable on a controlled diet, oral agents or insulin are acceptable.