It has been shown that benzoctamine possesses a spectrum of peripheral antagonistic activity towards various endogenous amines, including histamine and catecholamines, in vitro and in vivo similar to that of chlorpromazine. The serotonin-antagonistic activity in vitro of benzoctamine was some 10 times less than that of chlorpromazine. This was assumed to be the reason why benzoctamine was as effective as chlorpromazine in systemic anaphylaxis of the guinea-pig but less active than the latter in systemic anaphylaxis of the mouse.