Autoradiographic techniques were utilized to localize and to quantify angiotensin II (ANG) binding sites in rat forebrain. Specific, localized ANG binding sites were demonstrated in midline sagittal sections, corresponding to the entire anteroventral third ventricle (AV3V) area, including the nucleus preopticus medianus and the subependymal area of the anterior third ventricle from the nucleus preopticus medianus to the organon vasculosum laminae terminalis. A continuous band of ANG receptors extended dorsally from the nucleus preopticus medianus along the subependymal area of the third ventricle to the organon subfornicalis. Scatchard analysis performed with consecutive sections from single animals revealed a single class of high-affinity ANG receptors in both the organon subfornicalis and the organon vasculosum laminae terminalis. In addition, ANG receptors were localized in areas anatomically and physiologically related to the AV3V area, including the nuclei paraventricularis and periventricularis and the eminentia mediana. These results support the idea that ANG may act as both a hormone and a neurotransmitter in the central regulation of fluid balance and cardiovascular function, and suggest that the circumventricular organs are the most likely sites for an interaction between the peripheral and central ANG systems.