The injection into the 3rd ventricle of betha-nechol, carbachol and noradrenaline provoked the release of antidiuretic hormone (ADH) in the hydrated male rat, as indicated by a decrease in urine flow and free-water clearance, with an increased urinary electrolyte concentration, osmolality and conductivity. Atropine completely blocked the bethanechol- and carbachol-induced anti-diuresis, whereas phentolamine and pentolinium did not. On the other hand, the noradrenaline-induced antidiuresis was blocked by phentolamine, but not by atropine or pentolinium. Intraventricular injections of different doses of nicotine did not elicit any release of vasopressin. It is therefore concluded that separate synapses with the neurosecretory cell of both cholinergic muscarinic and α-adrenergic origin exist.