Antagonistic activity of cyproheptadine against common spasmogens, like acetylcholine, histamine, serotonin, bradykinin and angiotensin, was studied on isolated guinea-pig ileum. Cyproheptadine produced a reversible antagonism of non-competitive type and was most effective against serotonin. It was less potent against histamine, bradykinin and angiotensin and least potent against acetylcholine.