Electrical stimulation of the A1 noradrenergic region of the ventrolateral medulla produced synatic excitation (n = 19, 9%), inhibition (n = 5, 2%) or no effect (n = 184, 89%) in the activity of a total of 208 neurons in the subfornical organ (SFO) in male rats under urethane anesthesia. Almost all (n = 18) of the excitatory responses (n = 19) were blocked by microiontophoretically-applied phentolamine, an alpha-adrenergic antagonist, but not by timolol, a beta-adrenergic antagonist. The inhibitory response of all the neurons (n = 5) tested was prevented by iontophoretically applied timolol, but not by phentolamine. Approximately a half (n = 9) of SFO neurons that demonstrated the excitatory response to A1 region stimulation exhibited an increase in neuronal activity in response to hemorrhage (10 ml/kg b.w.t.), while remaining neurons (n = 10) were unresponsive. Hemorrhage did not cause any change in the activity of all the neurons (n = 5) that demonstrated the inhibitory response to A1 region stimulation. These results suggest that the medullary inputs to approximately 10% of SFO neurons tested are mediated by alpha-adrenergic excitatory and beta-adrenergic inhibitory pathways, and imply that a part of the excitatory pathways may transmit the peripheral baroreceptor information.