An intravenous formulation of lansoprazole, a proton pump inhibitor, is approved for use in patients with erosive oesophagitis who are temporarily unable to take oral lansoprazole. In healthy volunteers, oral and intravenous lansoprazole 30 mg/day were equivalent in suppressing basal and pentagastrin-stimulated maximum gastric acid output. Moreover, the mean 24-hour intragastric pH did not differ significantly following oral or intravenous administration of lansoprazole and was significantly higher with both formulations than with intravenous polyethylene glycol vehicle. After treatment for 7 days in patients with erosive oesophagitis, intravenous lansoprazole (30 mg/day) recipients had significantly lower median stimulated and basal gastric acid output measurements than placebo recipients. Median pentagastrin-stimulated gastric acid output levels were equivalent after 7 days treatment with intravenous or oral lansoprazole. Intravenous lansoprazole is generally well tolerated. All adverse events experienced by patients with erosive oesophagitis who received intravenous lansoprazole were mild or moderate in severity.