Visualization of [125I]ANF binding sites in rat brain by an autoradiographic technique demonstrated that these sites are highly localized in areas such as the olfactory bulb, subfornical organ, area postrema and nucleus tractus solitarius. This distribution suggests that certain cardiovascular effects of ANF could be centrally mediated and that the existence of brain ANF-related peptides should be considered. Finally, moderate densities of [125I]ANF binding sites are found in the rat and guinea pig eye while low densities are seen in pituitary and pineal gland.