To examine the hypothesis that abnormalities of noradrenergic innervation of hypothalamic pressor areas influence the pathogenesis of hypertension in the spontaneously hypertensive rat (SHR), the norepinephrine content of individual hypothalamic and brainstem nuclei was determined in SHR and control Wistar-Kyoto (WKY) rats at 5, 7, and 11 weeks of age. At 5 and 7 weeks of age, the norepinephrine content of the posterior hypothalamic area (PHA) of SHR was significantly greater than that of WKY controls. These changes occurred at a time when blood pressure was not significantly different between the two groups. The increase in the norepinephrine content of the PHA was accompanied by increases in the norepinephrine content of the A1 region and locus coeruleus in 5-week SHR. In seven week old animals, studies of norepinephrine turnover using α-methyl-p-tyrosine revealed no differences between SHR and WKY in turnover in the PHA. The increase in norepinephrine content of the PHA in the absence of changes in turnover is interpreted to indicate increased noradrenergic input to the PHA of SHR and supports the hypothesis that noradrenergic pathways to the PHA are important in the development of hypertension in this model. © 1984.