Gastrofensin AN 5 supresses the formation of ulcers in all experimental models. From the broad pharmacological studies of Gastrofensin AN 5 on this model it can be seen that even a dose of 0.100 mg/kg has a high antiulcer activity. The increase of the dose leads to a regular increase of the antiulcer activity, the highest suppression of the ulcer index being reaches at a dose of 1 mg/kg (86.15%). The comparative studies with Ranitidine and Cimetidine on the same experimental models of gastric ulcers show that Gastrofensin AN 5 possesses an antiulcer activity many times higher than that of the above-mentioned drugs.