We prepared a murine monoclonal antibody that recognized the Helicobacter pylori urease. Monoclonal antibody, U2, reacted with purified native urease in enzyme linked immunosorbent assay but it did not react in Western immunoblot analysis. Urease was immunoprecipitated with U2 bound to Staphylococcus aureus protein A, followed by elution and visualization by sodium dodecyl-sulfate polyacrylamide gel electrophoresis. The species and strain specificity of U2 were determined by biodot reaction with H. pylori, H. mustelae, Campylobacter spp., and other gram-negative bacteria. Monoclonal antibody, U2, was used for an indirect immunofluorescent stain of formalin fixed gastric biopsies from patients with H. pylori gastritis. The immunofluorescent stain showed spiral and coccoid forms of H. pylori within the gastric mucosa. U2 was specific for H. pylori and did not react with other tested bacteria. These findings suggest that antibody U2 might be of diagnostic value for specific immunofluorescence detection of H. pylori.