Angiotensin II (AII) sensitivity of neurons in the region of the organum vasculosum laminae terminalis (OVLT) was examined electrophysiologically using in vitro hypothalamic brain slices taken from 4-, 9- and 14-week-old spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. Micropressure application of AII, its competitive antagonist saralasin, and L-glutamate revealed that neurons in this region of SHR were significantly more sensitive to AII than cells in age-matched WKY preparations. Neuronal sensitivity to L-glutamate was similar between SHR and WKY rats at all ages. Following electrophysiological study, hypothalamic and cortical brain slices were assayed for 125I-labelled AII binding. AII receptor binding in the hypothalamic slices from SHR was elevated significantly above binding in WKY hypothalamic slices at 4, 9, and 14 weeks of age. In contrast, AII binding in cortical slices taken from SHR and WKY rats was similar. These data suggest that altered neuronal AII-sensitivity is not a consequence of hypertension development in SHR and may contribute to its development.