Centrally released arginine vasopressin (AVP) has been associated with various behavioural and cognitive effects, such as scent marking, aggression, and memory, which are believed to be mediated by the V1a subtype of the vasopressin receptor. Although the distribution of V1a receptors is conserved in a few brain regions, the pattern of expression of this receptor is, in general, highly species-specific. We have used receptor autoradiography with the linear V1a receptor ligand (125I-Phenylacetyl-D-Tyr(Me)-Phe-Gln-Asn-Arg-Pro-Arg-Tyr-NH2) to characterize the pattern of receptor binding in the rhesus monkey brain. Brain sites of V1a receptor synthesis were defined using in-situ hybridization. The regions of highest V1a receptor density included the prefrontal, cingulate, pyriform, and entorhinal cortex, as well as the presubiculum and mamillary bodies. In addition, V1a receptor binding and mRNA were detected in several regions reported to have V1a receptor in most rodents, including the amygdala, bed nucleus of the stria terminalis, lateral septum, hypothalamus and the brainstem. The distribution is consistent with a role for vasopressin in higher cognitive functions, especially memory, in primates.