Angiotensin II injected in small doses into the cerebral ventricles produces an increase in blood pressure and drinking behavior. The site of action for both of these effects was studied in 3 main experiments. (1) The response to several doses of angiotensin delivered to each ventricle was investigated with multiple ventricular cannulation. This revealed that the rostral ventricular system was involved in angiotensin II mediated responses. (2) CSF flow was limited by plugging specific anterior and posterior ventricular regions and then testing for angiotensin II induced drinking and pressor responses. This technique showed that the ventral anterior third ventricle must be reached by the peptide in order to produce either blood pressure or drinking effects. (3) In order to separate pressor components due to vasopressin release and sympathetic activation, hypophysectomized rats were also tested. The experiment showed that the pressor response to intraventricular angiotensin II is due to both sympathetic and pituitary hormonal components and both are dependent on sites sensitive to angiotensin in the anterior third ventricle. The ventraL anterior third ventricle or periventricular tissue surrounding it seems to be essential for both blood pressure and drinking responses to intraventricular angiotensin II.