OBJECTIVE To characterize the relationship between changes in renal blood flow and cardiac output induced by dopamine, hypothesizing that at low doses renal blood flow changes more than cardiac output. METHODS Anesthetized swine had renal blood flow and cardiac output measured during either continuous dopamine infusions (2 to 8 micrograms/kg per minute) or bolus dosing (1 to 16 micrograms/kg), and increases in both were compared. Two different fluid protocols were compared using constant dopamine infusions. In the constant pulmonary capillary wedge pressure protocol, intravenous fluids were titrated to keep this parameter constant. In the other protocol, fluid therapy was held constant at 10 mL/kg per hour. RESULTS With infusions, mean increases in renal blood flow and cardiac output were relatively equal. The maximum increase was 35% at 8 micrograms/kg per minute under the constant pulmonary capillary wedge pressure protocol, with no significant differences (P > .1) found between the change in renal blood flow and cardiac output at any dose in either protocol. With bolus dosing, renal blood flow increased significantly more than cardiac output at 1, 4, and 8 micrograms/kg (P < .05). CONCLUSIONS Disproportionate increases in renal blood flow compared with cardiac output at low bolus doses show initial renal responses to be independent of cardiac output. The infusion data suggest that renal responses exhibit tachyphylaxis or that cardiac output slowly accommodates to decreased total peripheral resistance.