The concentration of noradrenaline was measured in various regions of the brain and spinal cord of spontaneously hypertensive rats, stroke-prone spontaneously hypertensive rats and normotensive Wistar/Kyoto controls. Elevated noradrenaline levels were consistently found in the pons, cerebellum and spinal cord of the two hypertensive strains. These changes occurred both in young rats, during the early development of hypertension, and in mature rats, after establishment of the hypertension. The increases of cerebellar and spinal noradrenaline in mature stroke-prone rats could not be reversed by lowering blood pressure with hydralazine. The increased noradrenaline concentrations were not accompanied by increased tyrosine hydroxylase activity in the hypertensive rats. However, comparisons of noradrenaline turnover made using the catecholamine synthesis inhibitor, alpha-methyltyrosine, indicate an increased turnover of spinal noradrenaline in both hypertensive strains after establishment of hypertension. The results suggest that the activity of spinal noradrenergic nerves is augmented in genetically hypertensive animals.