The renal hemodynamic response to renal arterial dopamine infusions was compared in unanesthetized fetal (129-137 days gestation, full term 145 days), newborn, and adult sheep. Mean arterial blood pressure and heart rate remained unchanged during intrarenal dopamine infusions. Dopamine produced dose-related decreases in mean renal blood flow velocity in all three groups. When compared with adult sheep fetal sheep were slightly more sensitive to the vasoconstrictive effects of dopamine ED50 (mean effective dose ratio: fetus/ED50 adult = 0.368 +/- 0.047, P less than 0.05). Increases in mean renal blood flow velocity were not seen at any dose given (1-16 micrograms/kg body wt in fetuses, 2-32 micrograms/kg body wt in newborns and adults) until dopamine was infused during alpha- and beta-adrenoceptor blockade. The largest mean increase in renal flow velocity was 13 +/- 3, 16 +/- 3, and 17 +/- 4% in fetal, newborn, and adult sheep, respectively. cis-Flupentixol inhibited the vasodilation. This study demonstrates the presence of renal vasodilation following renal arterial dopamine infusions in fetal, newborn, and adult sheep when renal alpha- and beta-adrenoceptors are blocked. Vasodilator responses are similar in all three groups, and increases in renal blood flow velocity are small compared with that of other experimental models.