Immune mediators are involved in strain-specific manifestations of Helicobacter pylori infection, and the type of immune response is associated with production of PGE2, which in turn influences gastric acid secretion. Acid secretion plays a pivotal role, not only in the pattern of H. pylori-induced gastritis and its consequences, but also in nonsteroidal anti-inflammatory drug (NSAID)-induced gastropathies. Mice and their transgenic modifications are widely used in Helicobacter and eicosanoid research. Using [14C]aminopyrine accumulation and pylorus ligation, we aimed to study acid secretion in gastric gland preparations from the commonly used strains of BALB/c and C57BL/6 mice. We found that PGE2 does not inhibit acid secretion in gastric glands from C57BL/6 mice, in contrast to the expected antisecretory effect of PGE2 observed in BALB/c mice. In BALB/c mice the effect of histamine and carbachol was reduced by PGE2, whereas in C57BL/6 mice dose-response curves to these secretagogues were not affected. EP3 receptors are not involved in acid secretion in C57BL/6 mice, as confirmed by significantly lower expression of mRNA for the EP3 receptor. These contrary findings are important to the interpretation of the antisecretory role of eicosanoids in BALB/c and C57BL/6 mouse strains and the involvement of prostanoids in the etiology of Helicobacter-induced inflammation and NSAID-induced gastropathies. We propose that the lack of antisecretory effect of PGE2 observed in C57BL/6 mice could reflect the extent of Helicobacter-induced inflammation and status of acid secretion in response to anti-inflammatory drugs.