Gastric ulcers, located in the fundic area, appeared in pigs restrained during a 24 hrs period. Tbe development of tbese uleers was prevented by poreine calcitonin (P-CT) given intramuscuiarly or intragastraIly, at 5 hrs intervals, during tbe restraint period. P-CT increased significantly tbe pH of gastrie secretion at the end of restraint. In non-restrained fasting pigs, P-CT given intragastraIly strongly inbibited basal or gastrin-stimulated acid output. These results tend to indicate that P-CT prevented restraint-induced gastric ulcer in pigs, probably by inbibiting gastric HCl secretion.