This review discusses the role of the sympathetic nervous system in the pathogenesis and maintenance of human hypertension. Three points are emphasized: first, there are mechanisms by which the sympathetic nervous system can contribute to the long-term regulation of vascular resistance and arterial pressure in addition to the moment-to-moment regulation of arterial pressure; second, the microneurographic method for direct intraneural recording of sympathetic nerve activity in humans has provided mounting evidence for increased sympathetic neural activity in human essential and renovascular hypertension; and third, there are both peripheral reflex and humoral mechanisms that may contribute to sympathetic overactivity in human hypertension.