The immunohistochemical technique for the vasopressin localisation shows the presence of this hormone in neurons of the rat supra-chiasmatic nucleus. Different experimental conditions induce modifications of the supra-chiasmatic vasopressin, and, in the same time, the storage of immunoreactive peptide in the fibres terminating in the external zone of the median eminence. However, the supra-chiasmatic, supraoptic and paraventricular changes are not obligatory similar.