Two distinguishing features of the vasculature of the spontaneously hypertensive rat (SHR) are an increased sympathetic innervation and vascular smooth muscle hyperplasia. Evidence supporting the existence of hypernoradrenergic innervation and vascular smooth muscle cell hyperplasia is presented with emphasis upon the possible interrelationships between the two events. The results of experiments designed to explore this relationship are presented and include the determination of the role of endogenous nerve growth factor (NGF) and the influence of exogenous NGF on the development of sympathetic innervation of blood vessels and blood pressure change. Attention is focused upon elevated levels of 3-methylhistidine (a biochemical marker for contractile proteins) in the mesenteric vasculature of the SHR. The potential relationships between hypernoradrenergic innervation and increased concentrations of 3-methylhistidine are explored.