The administration of the neuropeptide W (NPW) and neuropeptide B (NPB) in rodents has been shown to influence the activity of a variety of autonomic and neuroendocrine systems. The paraventricular nucleus (PVN) is a major autonomic and neuroendocrine integration site in the hypothalamus, and neurones within this nucleus express the receptor for these ligands, NPB/W receptor 1 (NPBWR1). In the present study, we used whole cell patch clamp recordings coupled with single-cell reverse transcriptase-polymerase chain reaction to examine the effects of neuropeptide W-23 (NPW-23) on the excitability of identified PVN neurones. Oxytocin, vasopressin and thyrotrophin-releasing hormone neurones were all found to be responsive to 10 nm NPW-23, although both depolarising and hyperpolarising effects were observed in each of these cell groups. By contrast, corticotrophin-releasing hormone cells were unaffected. Further subdivision of chemically phenotyped cell groups into magnocellular, neuroendocrine or pre-autonomic neurones, using their electrophysiological fingerprints, revealed that neurones projecting to medullary and spinal targets were predominantly inhibited by NPW-23, whereas those that projected to median eminence or neural lobe showed almost equivalent numbers of depolarising and hyperpolarising cells. The demonstration of particular phenotypic populations of PVN neurones showing NPW-induced effects on excitability reinforces the importance of the NPB/NPW neuropeptide system as a regulator of autonomic function.