We studied the density of the angiotensin II (Ang II) binding site in discrete brain nuclei of 4-week-old and 14-week-old spontaneously hypertensive rats (SHR) and age-matched normotensive Wistar-Kyoto (WKY) control rats by autoradiographic binding techniques. Tissue sections were incubated in vitro with 3 nmol/l [125I]Sar1Ang and results were analysed by computerized microdensitometry and by comparison with 125I-standards. Both young and adult SHR (aged 4 and 14 weeks, respectively) had significantly higher Ang II binding site concentrations in the median preoptic nucleus (MPO), subfornical organ (SFO), paraventricular nucleus (PVN) and nucleus of the solitary tract (NTS) when compared to age-matched WKY control rats. No significant difference was found between strains in other brain areas such as the olfactory bulb, suprachiasmatic nucleus (SCh), inferior olive (IO) and area postrema (AP). It was observed that the concentration of Ang II binding sites increased with age in PVN of both SHR and WKY, while the number of binding sites in the MPO and IO decreased with age. In SHR, alteration in Ang II binding is restricted to brain nuclei involved in the central pressor action of Ang II and seems to be related to the development and maintenance of spontaneous hypertension.