Lansoprazole is a new proton pump inhibitor that was synthesized and developed in Japan. In study 1, we compared the acid secretion inhibitory effects of intravenous bolus injection and intravenous drip infusion of 30 mg twice daily of lansoprazole injection. In study 2, we compared 60 mg once daily and 30 mg twice daily of lansoprazole administered by intravenous bolus injection. Comparisons were made by the crossover method using 24-h intragastric pH monitoring in 10 healthy adult males. In both studies, lansoprazole significantly inhibited gastric acid secretion in comparison with control values. In comparison of administration methods, both intravenous bolus injection and intravenous drip infusion showed the same effectiveness. In the dose comparison, a single daily dose and two daily doses were both considered acceptable, but more reliable effects were achieved with two daily doses.