Low doses of exogenous dopamine (3 micrograms/kg/min) were administered intravenously to nine patients with essential hypertension and to six age-matched healthy volunteers. During infusion with dopamine, mean arterial blood pressure decreased in hypertensive patients whereas it did not change in normotensive subjects. Basal levels of sodium excretion were comparable in hypertensive and normotensive subjects. The natriuretic response to dopamine was significantly greater in hypertensive patients. Urinary and nephrogenous cAMP significantly increased in both normotensive and hypertensive subjects. The increase of nephrogenous cAMP was more pronounced in hypertensive patients than in normotensive controls. A significant correlation was found between nephrogenous cAMP and sodium excretion. The enhanced natriuretic response to dopamine in hypertensive patients may be due to increased cAMP formation in response to tubular dopamine receptor stimulation. This is in agreement with the hypothesis of either up-regulation or affinity changes of renal dopamine receptors in patients with essential hypertension, secondary to a decreased endogenous production of intrarenal dopamine.