Thirst elicited by the beta-adrenergic agonist isoproterenol in rats depends in part on the secretion of renin, the consequent synthesis of angiotensin II (ANG II), and the binding of circulating ANG II to dipsogenic receptors in the brain. These receptors probably reside in either of two forebrain circumventricular organs, the subfornical organ (SFO) or organum vasculosum laminae terminalis (OVLT). Experiments determined that lesions of the SFO, but not of the OVLT, reduced drinking induced by isoproterenol treatment. Competitive ANG II-receptor antagonism with sarthran reduced isoproterenol-induced drinking when the blocker was infused into the SFO but not when it was infused into the OVLT or into the lateral ventricles at a 25-fold greater dose. The findings confirm the widely held belief that renin-dependent thirst elicited by isoproterenol relies on ANG II binding to receptor sites at a circumventricular organ in the brain. The results demonstrate that this site is the SFO and not the OVLT.