Secretion of arginine-vasopressin (AVP) from the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei is induced by neurokinin B (NKB) and angiotensin. To characterize the mechanisms by which this occurs, we used immunohistochemical techniques to assess the ability of AVP-producing neurons to express NKB, NKB receptor (NK-3 receptor) and angiotensin II type 1 receptor (AT-1 receptor). Double fluorescence immunohistochemistry indicated that AVP-immunoreactive cell bodies in the PVN and SON, as well as their axon varicosities in the posterior pituitary, co-express NKB. Almost all AVP-neuron perikarya also expressed both the NK-3 receptor and AT-1 receptor. Thus, AVP-producing neurons in the PVN and SON, which are regulated by NKB, are themselves a source of NKB. Furthermore, the regulation of AVP release by these neurons by NKB and angiotensin II is mediated by the NK-3 receptor and the AT-1 receptor, respectively.