The in vivo binding of [³H]spiperone was measured in discrete areas of the hypothalamus in 7, 9 and 16 weeks old spontaneously hypertensive rats (SHR) and age matched normotensive Wistar Kyoto (WKY) controls. The specific binding of [³H]spiperone was significantly higher in the four different hypothalamic regions (H₁, H₂, H₃, H₄) that we have tested in 7 or 9 weeks old SHR than in age matched WKY controls. At 16 weeks a significant increase was only present in H₃. These results suggest that dopaminergic hypothalamic neurons might be implicated in the onset of hypertension in the rat.