SUMMARY Changes in the actirity of hypothalamic and brain-stem adrenergic neurons have been reported in young spontaneously hypertensive rats (SHR) prior to the development of hypertension. We have measured central α- and β-adrenoceptor concentrations in 4-week-old SHR and Wistar-Kyoto (WKY) controls by direct radioligand binding studies using [3H]prazosin (α1), [3H Clonidine (α2) and [123]iodohydroxybenzipindolol (β). The concentration of α2-adrenoceptors was significantly elevated in the bypothalamus of the SHR, 156.9 ± 10.4 compared with WKY, 119.4 ± 10.0 fmole/rag protein (n = 7, mean ± SEM,p< 0.0125). Alpha2-adrenoceptor concentrations in both the brain stem and cerebral cortex were similar in the two groups of animals. The increase in hypotbalamic adrenoceptors was specific for ai-adrenoceptors, since similar concentrations of α2and β-adrenoceptors were found in this region.