Objective:The renal effects of dopamine in critically ill patients remain controversial. Low-dose dobutamine has been reported to improve renal function. We compared the effects of various doses of dopamine and dobutamine on renal function in critically ill patients.Design:Prospective, single-blind, randomized study.Setting:University hospital, 19-bed multidisciplinary intensive care unit.Patients:Twelve hemodynamically stable patients with mild nonoliguric renal impairment.Interventions:Each patient randomly received four different doses of dopamine and dobutamine (placebo, 3, 7, and 12 μg/kg/min). Each infusion lasted for 4 hrs. Cardiac output and systemic hemodynamic variables were measured using a pulmonary arterial catheter at the beginning (HO) and the end (H4) of each infusion. The bladder was emptied at HO and H4 to determine urine volume and to collect samples.Measurements and Main Results:The cardiac index increased significantly with both dopamine and dobutamine (p< .001). Mean arterial pressure (MAP) increased, with the maximum effect of 20% seen with 12-μg/kg/min dopamine infusion (p< .01). No change in MAP was seen with dobutamine. Dobutamine infusions did not change any renal variables. Conversely, all dopamine infusions significantly increased diuresis, creatinine clearance, and the fractional excretion of sodium (p< .01). Creatinine clearance increased from 61 ± 16.9 (SD) mL/min to a maximum of 85.7 ± 30 mL/min at the 7-μg/kg/min dose; fractional excretion of sodium increased from 0.26% ± 0.28% to a maximum of 0.62% ± 0.51% at the 12-μg/kg/min dose (p< .01). During dopamine infusions, there was a significant relationship between MAP and creatinine clearance (p= .018).Conclusions:At all doses studied, 4-hr infusions of dopamine significantly increased creatinine clearance, diuresis, and the fractional excretion of sodium in stable critically ill patients. Conversely, dobutamine did not modify these variables. Although the level of MAP might partially contribute to the improvement in renal variables, it is more likely that the activation of renal dopamine receptors played a prominent role.