To obtain information about intestinal hemodynamics of healthy neonates, the authors assessed velocity and volume of blood flow with duplex Doppler sonography in the superior mesenteric artery (SMA) in 91 stable preterm and term neonates. Blood flow velocity in the SMA and estimated volume blood flow increased linearly with gestational age and increasing body weight. The mean estimated volume blood flow (+/- standard deviation) was 43 mL/kg/min +/- 13 and did not depend on differences in body weight. The authors also assessed blood flow velocity in the SMA and volume blood flow in 18 infants with conditions that may affect blood supply to the bowel. Twelve infants who were small for gestational age appeared to have an abnormally low resistance of the vascular bed of the SMA during the 1st days of life, as compared with stable appropriate-for-gestational-age infants matched for gestational age. Three of six term neonates with cardiovascular abnormalities had left ventricular outflow obstruction and an abnormal blood flow velocity waveform of the SMA, suggesting a decrease in blood supply to the bowel. The results of this study may help in evaluations of intestinal perfusion in infants with abnormal conditions.