Beta-Adrenergic stimulation with isoproterenol hydrochloride in animals causes an antidiuresis similar to antidiuretic hormone. This investigation was undertaken to determine whether isoproterenol inhibits water diuresis in man. Seven young male volunteers were studied during water diuresis in three phases: (1) water-loading, (2) water-loading plus isoproterenol, and (3) water-loading plus isoproterenol plus propranolol hydrochloride. Antidiuresis occurred 20 minutes following isoproterenol infusion (0.03mug to 0.06mug/kg/min) from a mean of 19.4 to 2.0 ml/min. We found that antidiuresis is due to the hormonal (antidiuretic hormone) and nonhormonal changes (decreased glomerular filtration rate and renal plasma flow). These in turn are due to the cardiovascular effects of the drug.