Transcutaneous Doppler ultrasound measurements were made of the superior mesenteric artery of 22 preterm infants (mean birth weight 600-2580 g) to investigate the response of intestinal blood flow to feeding. Analysis of the data in relation to milk intake showed a significant change in peak velocity and mean velocity; peak velocity before feeding increased from a mean baseline value of 34 cm/s in fasting infants to 46 cm/s when less than 50 g milk/kg body weight a day were given, and up to 56 cm/s when 50 g or more of milk/kg body weight a day were given. The corresponding values for mean velocity were 10, 15, and 22 cm/s, respectively. The pulsatility index decreased from 0.94 to 0.90 and 0.86 as milk volumes were increased. This investigation showed characteristic changes in the response of intestinal blood flow to feeding: 15 minute peak velocity and mean velocity rose significantly 15, 45, and 90 minutes after feeding, whereas the pulsatility index fell. Flow rate peaked 45 minutes after feeding.