Antiulcer effects of pantoprazole, a proton-pump inhibitor, on water-immersion restraint stress (WIRS)-, alcohol (ethanol)- and pylorus ligation-induced gastric ulcers were investigated in male rats. Rats were orally administered with pantoprazole 30 min prior to exposure to various types of ulcer inducers. In stress-induced ulcer model, rats were subjected to WIRS at 22℃ for 4 hours, and the degree of ulcer (in mm) was evaluated. In alcohol-induced ulcer model, rats were orally administered with pure (100%) ethanol (1 mL/kg), and the ulcer lesions were measured 1 hour after ethanol challenge. In pylorus ligation-induced ulcer model, rats were subjected to pylorus ligation, and the degree of erosions and ulcers was scored 17 hours after the operation. Pantoprazole attenuated the ulcer lesions induced by WIRS in a dose-dependent manner, exhibiting a median effective dose (ED(50)) value of 0.78 mg/kg. By comparison, pantoprazole was effective at relatively-high doses for the improvement of ethanol-induced ulcers, showing an ED(50) value of 20.5 mg/kg. Notably, pantoprazole was practically ineffective (ED(50)>50.0) in pylorus ligation model. Taken together, it was confirmed that pantoprazole showed inhibitory activity on gastric ulcers induced by stress and alcohol, but was ineffective on pylorus ligation-induced ulcer. Therefore, the results indicate that proton-pump inhibitors including pantoprazole might reveal highly-different effects according to the type of ulcer inducers, and that the prescription of antiulcer agents should be carefully selected.