Conscious rats were infused intravenously with either angiotensin II (30-55 pmol/kg/min), isotonic saline or phenylephrine for 2 h, then killed. Fos was identified by immunohistochemistry in the brains. Fos expression occurred in many neurons of the subfornical organ and organum vasculosum of the lamina terminalis (OVLT) with angiotensin infusion but not with isotonic NaCl or phenylephrine. Fos immunoreactivity was induced in cells in several medullary, hypothalamic and limbic structures with infusions of angiotensin II or phenylephrine at pressor doses. The results suggest that blood-borne angiotensin II at physiological levels causes angiotensin receptive neurons in the subfornical organ and OVLT to express Fos. Activation of baroreceptor pathways may also induce Fos expression at several other sites.