Anatomical studies have suggested that the posterior pituitary peptide, vasopressin (VP, antidiuretic hormone) may be released at central neural sites other than the neurohypophysis. Immunohistochemical techniques allow VP to be visualized at numerous sites in the central nervous system (CNS). VP can also be measured in cerebrospinal fluid (CSF). Some of the stimuli which evoke VP release from the posterior pituitary may also elevate CSF VP levels. VP may play an important part in a variety of CNS functions. Substantial evidence exists implicating VP in learning and memory processes. VP may have a role in cardiovascular regulation through central pathways. Further, VP appears to act on the regulation of body temperature during fever. Other areas of central regulation where VP may be important include circadian rhythmicity, control of water intake, control of permeability of brain capillaries to water, central regulation of ACTH release and nociception. It appears that at least some of these central effects of VP involve an interaction with catecholaminergic neurotransmission.