Fos immunoreactivity in the rat brain after intracerebroventricular (ICV) angiotensin II (ANG II) was compared with that induced by intravenous ANG II. ANG II was infused into the lateral ventricle (at 1 ng/min) or femoral vein (at 5 micrograms/h) of conscious rats. After 90 min, rats were killed and Fos was detected by immunohistochemistry. Both infusions caused Fos immunoreactivity to be present in the lamina terminalis, hypothalamic supraoptic, and paraventricular nuclei, bed nucleus of the stria terminalis, and central amygdaloid nucleus. However, distributions of Fos immunoreactivity within the lamina terminalis differed with the different routes of infusion. Intravenous ANG II caused intense Fos immunoreactivity mainly in the subfornical organ (SFO) and organum vasculosum of the lamina terminalis (OVLT). By contrast, ICV ANG II caused intense Fos immunoreactivity predominantly in the median preoptic nucleus and juxtaventricular neurons of the SFO and OVLT. These results suggest that IV ANG II induces behavioural and endocrine responses by direct actions on the SFO and OVLT, whereas ICV ANG II directly stimulates neurons in the median preoptic nucleus as well neurons in the SFO and OVLT.