The macrophage migratory inhibitory factor (MIF) plays a pivotal role in inflammatory and immune diseases; however, its role in gastrointestinal diseases has not been clarified. This study intended to determine the expression of MIF, by gastric epithelial cells, T cells, and macrophages, in Helicobacter pylori-induced gastritis. Sixty-four patients (30 males, 34 females; mean age, 47 years) referred for upper endoscopy were recruited. Biopsy specimens from the gastric antrum and corpus were obtained for (1) detection of H. pylori and histological examination, (2) single and double immunostaining to test for expression of MIF protein in epithelial cells, T cells, and macrophages, and (2) in situ hybridization for expression of MIF mRNA within the lamina propria. In mucosal specimens from each of the 2 sites, both the percentage of MIF(+) epithelial cells and the numbers of MIF mRNA(+) inflammatory cells, MIF(+) T cells, and MIF(+) macrophages were significantly higher in H. pylori-positive patients than in H. pylori-negative patients. Overall, the percentage of MIF(+) epithelial cells and the numbers of MIF mRNA(+) cells, MIF(+) T cells, and MIF(+) macrophages were higher in the antrum than in the corpus. The percentage of MIF(+) epithelial cells and the numbers of MIF mRNA(+) cells, MIF(+) T cells, and MIF(+) macrophages increased in chronic gastritis, but, in the absence of H. pylori infection, this increase disappeared for all except MIF(+) T cells. Therefore, H. pylori infection is associated with increased expression of the MIF protein and MIF mRNA in gastric epithelial and inflammatory cells; along with other cytokines, MIF may play a significant role in gastric inflammation related to H. pylori infection.