The aim of this study was to determine the in vitro activity of ranitidine, ebrotidine, bismuth citrate, omeprazole, and lansoprazole against 113 clinical isolates of Helicobacter pylori cultured from gastric biopsies. An agar dilution method using Mueller-Hinton agar plus 7%, horse blood, an inoculum of 10(6) cfu/spot, and incubation in a CO2 incubator for 2 to 5 days was used. The minimum inhibitory concentrations for 50 and 90% of the isolates tested, respectively, were as follows: ranitidine, 1024 and 1024 mg/l; ebrotidine, 64 and 256 mg/l; bismuth citrate, 1 and 4 mg/l; omeprazole, 16 and 16 mg/l; and lansoprazole, 1 and 1 mg/l. Ebrotidine was more active than ranitidine, and lansoprazole was the most active compound against the Helicobacter pylori isolates tested.