The oral administration of 2.5 mg of the dopamine (3,4-dihydroxyphenethylamine) agonist bromoergocriptine enhanced the osmotically stimulated rise in plasma [arginine]vasopressin ([Arg]VP) concentrations in five normal human subjects. 2. This finding lends support to the suggestion that the osmotically induced release of [Arg]VP is under dopaminergic control in man.