Esomeprazole, a new proton pump inhibitor, is the S-isomer of omeprazole and is the first such inhibitor to be developed as a single isomer. Esomeprazole provided better control of intragastric pH than omeprazole, lansoprazole and pantoprazole in trials conducted in patients with gastro-oesophageal reflux disease (GORD) or healthy volunteers (n = 20 to 115). In 2 large randomised, double-blind multicentre trials esomeprazole 20 and/or 40mg for 8 weeks produced higher healing rates of erosive oesophagitis and better symptom control than omeprazole 20 mg in patients with GORD. Esomeprazole 10, 20 or 40mg once daily for 6 months maintained healing versus placebo (p < 0.001) in patients with endoscopically confirmed healed erosive oesophagitis in 2 large randomised, double-blind multicentre trials. Similarly, symptom-driven on-demand use of esomeprazole effectively controlled symptoms of GORD (heartburn) for 6 months in 2 large placebo-controlled trials. Esomeprazole-based triple therapy for 7 days was as effective for eradication of Helicobacter pylori as longer omeprazole-based therapy in 2 randomised double-blind trials including about 450 patients each. Endoscopically confirmed ulcer healing 4 weeks after treatment initiation was reported in about 90% of patients with active duodenal ulcer in both treatment groups. Esomeprazole-based triple therapy for 10 days was more effective than esomeprazole plus clarithromycin for eradication of H. pylori in 233 patients.