Gastric parietal cells are important in acid secretion, but it is unclear which cells throughout the gastric gland have the highest secretion potency. Here, we used immunohistochemical methods with anti-H + , K + -ATPase, phosphoryl ezrin and CD44 antibodies to study the distribution of gastric acid secretion activity. Stomach tissues from freely fed and starved rats were cryofixed for light microscopy or fixed by high-pressure freezing for electron microscopy. Parietal cells from freely fed animals corresponded to the active secretion phase and to the inactive resting phase from starved rats. Anti-H + , K + -ATPase and anti-phosphoryl ezrin labeling were observed on the membrane of the intracellular canaliculi and the tubulovesicle from freely fed rats, while cells from starved animals showed weak labeling with anti-phosphoryl ezrin antibody staining. Morphometrical analysis at the electron microscopic level was performed on active and inactive acid secretory phases between the upper and base regions of the gland. H + , K + -ATPase and CD44 were distributed on both sites of the microvillous and tubulovesicle membrane in the same cells, but phosphoryl ezrin localized predominantly on the microvillous membrane in active cells of the glandular neck and upper base. Therefore, the highest secreting potency appeared to be in cells of the glandular neck and upper base.