Yohimbine in fairly high doses in animals exerts adrenolytic effects and in still higher doses produces sympathetic nerve blockade. The yohimbine blockader of cardiovascular responses to adrenaline is not altered by any of a considerable number of anesthetic agents. An antiserotonin activity of yohimbine has been demonstrated on isolated strips of carotid artery. Yohimbine has been shown to suppress carotid cardiovascular reflexes in animals. Local anaesthetics properties have been shown for yohimbine and little direct action on smooth muscle is claimed. The central nervous system actions are reported to be less prominent than those of the ergot alkaloids and benzodioxanes. Yohimbine significantly prolonged the sleeping time produced by barbiturates. Although long considered an “aphrodisiac”, present evidence provides no endocrine basis for this effect, the observed response appears to depend upon circulatory changes.