Helicobacter pylori urease is absorbed into the gastric mucosa at sites of inflammation, but whether the enzyme activates mucosal macrophages is not known. Because mucosal macrophages differ phenotypically and functionally from blood monocytes, whether recombinant H. pylori urease (rUrease) activated purified lamina propria macrophages in vitro was investigated. rUrease (1-10 μg/mL) induced primary mucosal macrophages to produce interleukin (IL)-1β, IL-6, and tumor necrosis factor (TNF)-α but not IL-8 proteins in a dose-dependent manner (P<.05 to P<.001). Quantitative reverse transcriptase-polymerase chain reaction using capillary electrophoresis laser-induced fluorescence showed that rUrease (0.1-10 μg/mL) also induced dose-dependent expression of IL-10, IL-6, and TNF-α but not IL-8 mRNA (P< .05), suggesting that rUrease-induced production of certain cytokines is regulated at the level of gene transcription. These findings indicate that the ability of H. pylori urease to activate mucosal macrophages, resulting in production of proinflammatory cytokines, may be involved in the pathogenesis of H. pylorj-associated mucosal inflammation. © 1998 by the Infeclious Diseases Society of America. All rights reserved.