The content of arginine vasopressin and oxytocin in various extrahypothalamic sites of the rat brain and spinal cord was determined by specific radioimmunoassays after lesions had been made in either the paraventricular (PVN), supraoptic (SON) or suprachiasmatic nuclei (SCN). In some animals all 3 nuclei were destroyed together. The PVN provided a considerable amount of the vasopressin innervation of the solitary tract nucleus, and most of that in the spinal cord. Oxytocin was removed from some areas after lesions of the PVN and, again, most of this peptide was lost from the spinal cord. Lesions of the SCN did not appear to be followed by significant quantitative changes in either hormone in any of the areas studied. Lesions of the SON resulted in loss of oxytocin, particularly in the periventricular grey and some other areas, suggesting that extrahypothalamic projections from this nucleus may be more important than was previously assumed. Lesions of all 3 nuclei which included destruction of accessory hypothalamic nuclei resulted in a much more widespread loss of vasopressin and oxytocin, but there was preservation of both peptides in the dorsal raphe nucleus and much of those present in the locus coeruleus. It is concluded that the contribution of the classical hypothalamic nuclei to the extrahypothalamic content of vasopressin and oxytocin in rat brain is less than was originally believed, and that there are areas of the brain such as the locus coeruleus and dorsal raphe nucleus in which the source of these peptides may be outside the hypothalamus.