Rats with lesions centered on the ventral stalk of the subfornical organ (SFO) were used to characterize the participation of this structure in the control of drinking. It is concluded that the SFO does indeed play some minor role in the mediation of drinking following intraventricular injections of angiotensin. Further, it is shown that lesions of the SFO, but not lesions of the adjacent septal-hippocampal tissue, attenuate osmotic thirst elicited by two doses of hypertonic saline. Diminished drinking responses following water deprivation, and normal feeding responses following food deprivation, underscore the importance of the SFO for drinking behavior in general, and an expanded role for the SFO in fluid regulation is suggested. However, some incidental observations suggest that the SFO is less than an equal partner with structures in the AV3V region in the overall control of water balance.