Binding sites for arginine-vasopressin (AVP) and oxytocin (OT) were detected in neuroanatomically defined regions of rat brain by using in vitro incubation of 32 micron brain sections with the tritium-labelled ligands and autoradiography with LKB Ultrofilm. Sites were quantified by computerized densitometry of the film images. The highest amount of [3H]AVP-labelled binding sites were observed in the ventral subiculum of the hippocampus, central amygdala nucleus, lateral septum, olfactory nucleus and nucleus tractus solitarii, while the dentate gyrus contained a large amount of low affinity binding. The binding pattern of [3H]OT was more discrete. Relatively high concentrations of OT binding sites were observed in the central amygdala, ventral subiculum and olfactory nucleus. The lateral septum and the nucleus tractus solitarii were virtually devoid of displaceable OT binding while no significant association of OT with the dentate gyrus was found. The topography of binding sites for neurohypophyseal hormones corresponds to the localization of responsive sites in behavioural, biochemical and electrophysiological studies.