Helicobacter pylori urease was recovered as a single peak by DEAE-Sepharose column chromatography and Sephacryl S-200 gel filtration. The purified urease was obtained by fast protein liquid chromatography using a Mono Q column. The purified urease preparation gave a single band in polyacrylamide gel disc electrophoresis. Latex particles were sensitized with anti-urease immunoglobulin. The sensitized latex particles were agglutinated with the purified urease and by cell sonicates obtained from 55 strains of H. pylori which were isolated from the gastric mucosa of patients with gastric and duodenal disorders, while they did not react with those obtained from related bacteria known to be urease producers, such as Helicobacter mustelae and urease- positive "Campylobacter lari variants", or by urease of some strains of Enterobacteriae. We have developed a specific and sensitive method for detecting the urease by using the reversed passive latex agglutination technique, in order to identify of the organism.