Objective: To study the effects of dopamine on renal, mesenteric, and cerebral blood flow in sick preterm neonates. Study design: The pulsatility index was used to assess the dopamine-induced changes in renal, mesenteric, and cerebral blood flow by means of color Doppler ultrasonography in 23 nonhypotensive preterm neonates (birth weight: 981 ± 314 g; postnatal age: <2 days). Dopamine was given at a dose of 6.1 ± 3.0 μg/kg per minute to combat oliguria, impaired peripheral perfusion, or both. Blood flow velocity measurements were made before and during dopamine administration, with each patient serving as his or her own control subject. Results: Dopamine significantly increased blood pressure and urine output. Dopamine decreased the pulsatility index in the renal artery (2.98 ± 1.18 vs 1.68 ± 0.45; P < .05) while the pulsatility index in the superior mesenteric and medial cerebral artery was not affected. Thus renal blood flow increased while mesenteric and cerebral blood flow remained unchanged during dopamine treatment. The increase in renal blood flow was independent of the blood pressure changes. Conclusions: These findings suggest a functionally mature renal, but not mesenteric, vasodilatory dopaminergic response in the preterm neonate. The observations also indicate the lack of an effect of low- to medium-dose dopamine on cerebral hemodynamics in the nonhypotensive preterm neonate. (J Pediatr 1998;133:728-34)