An investigation of antihistaminic activity and gastric ulceration has been done in guinea pigs and rats. Gastric ulcers were produced in guinea pigs by histamine and restraint procedures, while pyloric-ligation and reserpine were used in rat experiments. Brompheniramine, AHR-224-B, tripelenamine HCl, cyproheptadine HCl and promethazine HCl were effective in preventing histamine-induced ulceration in guinea pigs. Glycopyrrolate, a potent anticholinergic, was ineffective. Brompheniramine, the most potent antihistamine (against histamine-induced ulceration), was further investigated for its effects on gastric ulceration induced by other procedures. In restraint-induced ulcers in guinea pigs, the drug was without protective effect. When the gastric ulceration was produced in rats by pyloric-ligation or reserpine, this antihistamine, in contrast to glycopyrrolate, did not exert a protective action. These studies show that several antihistamines are effective antagonists to histanine-induced gastric ulceration in guinea pigs. The effectiveness of certain pharmacological agents (antihistamine or anticholinergic) in preventing gastric ulceration is determined to a large degree by the method employed to produce the ulceration. © 1969.