The aim of this study was to demonstrate the effect of acid inhibitor on the function and ultrastructure of gastric parietal cells in rats under immersion and restraint stress. Thirty two male SD rats were randomly divided into control, stress, omeprazole and cimetidine treated groups. The gastric mucosal ulcer index (UI) and gastric juice pH were measured. The ultrastructural changes of parietal cells were observed by transmission electronic microscopy (TEM). The UI was decreased and the pH value was increased obviously in omeprazole and cimetidine treated groups compared with stress group ( P