Helicobacter pylori (H. pylori) infection in the stomach is etiologically closely associated with chronic active gastritis, peptic ulcer, gastric cancer and gastric mucosa-associated lymphoid tissue lymphoma. In this study, we examined the antibody responses and cytokine profiles of three strains of mice (BALB/c, C3H/He, and C57BL/6) infected with H. pylori. Following this, correlations between host-immune reactions and intensity of inflammation were analyzed. H. pylori (ATCC43504) was intragastrically administered once a week to the mice from 4 weeks of age, and they were sacrificed at the ages of 4 and 7 months. In these mice, we examined the histology of the stomach, antibody titers against H. pylori, and serum levels of cytokines (IL-4, IL-10, TNF-alpha, IL-2 and Interferon-gamma). In BALB/c mice, inflammation of the stomach was minimal. Inflammation was observed in 63.6% of C57BL/6 mice and 33.3% of C3h/He mice. In C57BL/6 and C3H/He mice, all the cytokines tended to increase. In contrast, BALB/c mice were inactive in cytokine production except for IL-2. Two C3H/He mice developed severe inflammation with lymph follicles; one showed a response largely typical of Th-1, and the other showed a response largely typical of Th-2. Although a definite correlation was not shown between Th-1/Th-2 response evaluated by cytokine production and intensity of inflammation, it appears that in H. pylori-induced inflammation both cell-mediated (Th-1) and humoral (Th-2) immunity play a role in pathogenesis.