BACKGROUND: Acid suppression is the mainstay of therapy in gastro-oesophageal reflux disease. Esomeprazole 40 mg is more effective than lansoprazole 30 mg in healing mucosal lesions in severe erosive reflux oesophagitis. However, data comparing esomeprazole with lansoprazole in patients with complications of gastro-oesophageal reflux disease, such as ulcerative reflux oesophagitis and Barrett's oesophagus, are lacking. AIM: To compare the efficacy of esomeprazole and lansoprazole at their standard dosages in suppressing oesophageal acid exposure in complicated gastro-oesophageal reflux disease. METHODS: Thirty patients with complicated gastro-oesophageal reflux disease (7 with ulcerative reflux oesophagitis and 23 with Barrett's oesophagus), randomly assigned to receive 40 mg esomeprazole (n=16) or 30 mg lansoprazole (n=14) once daily, underwent oesophageal 24-h pH monitoring while on therapy. Total, upright diurnal and supine nocturnal percentage acid reflux time were assessed. RESULTS: Esomeprazole was significantly more effective than lansoprazole in decreasing oesophageal acid exposure. Normalisation of both total and supine nocturnal percentage acid reflux time was obtained in 12 of 16 (75%) patients treated with esomeprazole but only in 4 of 14 (28%) cases treated with lansoprazole (p=0.026). CONCLUSIONS: Normalisation of oesophageal acid exposure can be achieved in the majority of complicated gastro-oesophageal reflux disease cases with esomeprazole 40 mg once daily.