The neurohypophyseal hormones vasopressin and oxytocin modulate memory processes. Vasopressin facilitates, while oxytocin attenuates memory consolidation and retrieval. These influences are located in different regions of the molecules. Thus, the neurohypophyseal hormones act as precursor molecules for neuropeptides involved in memory processes. The covalent ring structures of both vasopressin and oxytocin mainly affect consolidation; the linear parts, retrieval processes; while nearly the whole oxytocin or vasotocin molecule is needed for attenuation of consolidation and retrieval. Regional studies, utilizing microdissection techniques in combination with a sensitive radioenzymatic catecholamine assay, revealed a distinct pattern of effects on cerebral alpha-methyl-p-tyrosine methylester-induced catecholamine disappearance following intraventricular vasopressin administration in limbic midbrain structures. In situations in which the amount of bioavailable vasopressin in the brain is absent, as is the case in the Brattleboro rat with hereditary diabetes insipidus, or neutralized in normal Wistar rats following the intraventricular administration of antivasopressin serum, regional catecholamine disappearance in most cases is altered in a direction opposite to that observed after intracerebroventricular vasopressin administration. These results indicate that vasopressin modulates memory processes by modulation of neurotransmission in distinct catecholamine systems. Recent experiments suggest that the influence of vasopressin on memory consolidation is mediated by the dorsal noradrenergic bundle via terminal regions of this bundle.