We have examined the disposition of catecholamines in cardiac tissue, mesenteric arteries and ganglia from normotensive Wistar-Kyoto rats (WKY), spontaneously hypertensive rats (SHR) and stroke-prone spontaneously hypertensive rats (SHR-SP). The norepinephrine (NE) contents of mesenteric arteries from all three strains of rats adhered to a pattern which was characterized by the largest concentrations of the catecholamine in arteries from SHR and SHR-SP rats, and the smallest values present in mesenteric arteries from WKY rats. This pattern of NE disposition was not present in either ganglia or cardiac tissue from the three strains of rats. The results highlight two features of the hypernoradrenergic hypothesis in the SHR. Firstly, the enhanced NE contents observed in the blood vessels of the two hypertensive strains are not consistently increased in sympathetic cell bodies or cardiac tissue. Secondly, the significantly enhanced concentrations of NE in the vasculature parallel the elevated direct arterial blood pressure in the two strains of hypertensive rat when compared with the normotensive strain.