The effect of cocaine on the pressor response to some sympathomimetic amines before and after the acute reserpinization in dogs, anesthetized with pentobarbital sodium (i. v) in combination with morphine hydrochloride (s. c) and atropine sulfate (s. c), was investigated.Administration of cocaine suppressed the pressor effect of ephedrine and related compounds ; but administration of reserpine considerably removed the suppressive action of cocaine, though some difference was found according to the stage. However, the suppressive action of cocaine on tyramine was more intense than other drugs. In experiments in which no ephedrine-like compounds in the control dose were administered before cocaine, blood pressure rose after reserpine was restored, especially in the case of tyramine.