In 15 preterm infants with symptomatic patent ductus arteriosus, blood flow velocity changes in the superior mesenteric artery were investigated with Doppler ultrasound just before and during the first 12 hours after a single dose of indomethacin. Indomethacin administration led to an instantaneous decrease in all infants of temporal mean flow velocity in the superior mesenteric artery, which was maximal 10 minutes after administration of indomethacin, followed by a more sustained recovery, slightly greater than baseline values, 12 hours after indomethacin treatment. Simultaneously determined temporal mean flow velocity of the anterior cerebral artery, used as an indicator of changes in cerebral blood flow, had a similar pattern as in the mean flow velocity in the superior mesenteric artery (r = 0.49; p less than 0.001). Our data suggest that indomethacin lowered blood supply to the bowel, similar to its action on cerebral blood flow.