Rats with transections of subfornical organ (SFO) efferent projections failed to drink to intravenous angiotensin-II (AII) but responded to intracellular dehydration and water deprivation and suppressed drinking when food deprived. However, the transected rats were polydipsic and polyuric. Thus SFO efferent projections mediate AII-induced drinking and may be involved in the regulation of body fluid balance.