The purpose of the present study was to examine the effect of the alpha 2-adrenoceptor antagonists yohimbine and idazoxan on kidney function in intact Sprague-Dawley rats and in Brattleboro rats with familial hypothalamic diabetes insipidus. Both drugs, injected intravenously at 0.5 mg/kg, led to a marked decrease of urine flow, sodium, potassium and chloride excretion in both strains of rats. Glomerular filtration rate and effective renal plasma flow did not change significantly in either strain. The study demonstrates that the alpha 2-adrenoceptor antagonists induce an antidiuretic effect without changes in renal hemodynamics. Antidiuretic hormone does not play a role in yohimbine- or idazoxan-induced antidiuresis. The data suggest a role for alpha 2-adrenoceptors in the renal tubular handling of water and salt.