Nor-epinephrine, a pressor amine known to exist normally in the mammalian body, is identical with epinephrine except for the absence of a methyl group in its chemical structure. Since methylation occurs readily in the body, it has been suggested that nor-epinephrine functions chiefly as a precursor to epinephrine (1-5). Nevertheless, it possesses potent pharmacologic properties which differ in many respects from those of epinephrine (6-9). Epinephrine raises systolic blood pressure, increases cardiac output and accelerates the heart rate; it constricts blood vessels in certain areas of the circulatory bed, dilates them in others, with an over-all effect of dilatation and a decrease in total peripheral vascular resistance. Nor-epinephrine increases systolic and diastolic blood pressure, has little or no effect on cardiac output and decreases cardiac rate. It constricts blood vessels in all areas of the circulation in which its effect has been studied.Little is known, however, of the effects of norepinephrine and epinephrine upon the cerebral circulation in man. A clear understanding of their effects on this important segment of the circulation should provide information bearing on a number of physiologic, pathologic, and therapeutic questions.