The administration of tremogenidine doses of Tremorine, 1,4-dipyrrolidino-2 butyne, is followed by a significant decrease in the concentration of norepinephrine in the brain stem of three common laboratory species. The change in the concentration proceeds at a rate which coincides with the occurrence of the tremor in each of these species. In the rat, the change in norepinephrine is followed by a progressive increase in the concentration of 5-hydroxytryptamine in the brain stem. Bilateral adrenalectomy in the rat enhances the Tremorine-induced changes in the concentration of norepinephrine and antagonizes the increase in the concentration of S-hydroxytryptamine.