A technique for the preparation and recording of mammalian supraoptic nucleus neurosecretory neurons maintained in vitro through perfusion of the anterior cerebral artery is described. A slice of basal diencephalon measuring approximately 8 X 8 X 2 mm that includes the pituitary stalk and medial preoptic-anterior periventricular area permits stable extracellular and intracellular recordings of antidromic and orthodromic activity from identified supraoptic neurosecretory cells. The preparation as described remains viable for 10-12 h, permits tests on osmotic sensitivity of neurosecretory cells, the possibility of synaptic isolation through addition of excess magnesium and tests on neuropharmacology of SON neurons during the addition of putative neurotransmitter substances. The principle advantage of this perfused preparation over in vitro hypothalamic slice recordings is the maintenance of connections that permit identification of neurosecretory neurons and study of certain synaptic connections with neurophysiological and pharmacological techniques.