The relationship between the maintenance of hypertension and the central noradrenergic nervous system activity in spontaneously hypertensive rats (SHR) was studied. The norepinephrine turnover rates in 5 brain areas; telencephalon, hypothalamus/thalamus, midbrain, pons/medulla, cerebellum as a measure of noradrenergic neuronal activity were measured at the ages of 14 weeks in SHR and normotensive Wistar rats. In 14-week old SHR, blood pressure was significantly higher than in normotensive rat, and central norepinephrine turnover rates were significantly greater in telencephalon, hypothalamus/thalamus, midbrain. There were no differences between norepinephrine turnover rates in pons/medulla, cerebellum of SHR and those of normotensive rats.