Twenty-one strains of Campylobacter pylori (Campylobacter pyloridis) were tested for susceptibility to norfloxacin and other agents by the serial agar dilution method. Ampicillin (MIC for 90% of isolates [MIC90], 0.016 μg/ml) and famotidine (MIC90, >1,024 μg/ml) were, respectively, the most and the least active of the agents tested. Norfloxacin (MIC90, 1 μg/ml) and imipenem (MIC90, 0.125 μg/ml) were substantially active against this organism.