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Previous studies have used new angiotensin II (AII) receptor subtype selective compounds to localize AII receptor subtypes within discrete rat brain nuclei. The purpose of this autoradiographic study was to extend these preliminary findings and provide a comprehensive analysis of AII binding sites in 22 rat brain nuclei and the anterior pituitary, to include estimates of the binding affinity for ¹²⁵I sar¹ ile⁸ AII (¹²⁵I SIAII) at each nucleus, and determine the fractional distribution of each subtype at each nucleus. Estimates of K_D in separate experiments revealed that AT₁ nuclei had a consistently higher affinity for ¹²⁵I SIAII than AT₂ nuclei (0.66 vs. 2.55 nM). Displacement of subsaturating concentrations of ¹²⁵I SIAII by 10^–8–10^–4M DuP753 (selective for the AT₁ subtype) or PD123177 (selective for the AT₂ subtype) indicated that approximately half of the brain regions surveyed contained predominantly AT₁ sites …