To determine whether initial mesenteric hypoperfusion predisposes to NEC, we assessed superior mesenteric artery (SMA) peak systolic velocities (PSV) relative to those in the coeliac access (CA) using duplex pulsed Doppler ultrasound, in a group of infants with perinatal complications which placed them at increased risk of NEC. The ratio of PSV in these adjacent vessels (CA/SMA) was used to determine relative downstream resistance in the SMA. We studied two control groups: i) 14 term neonates (mean wt 3.3 kg); ii) 18 preterm infants with no history of perinatal asphyxia (mean wt 1.6 kg; 27-35 wk). The study group comprised 27 infants at increased risk of developing NEC who had sustained perinatal asphyxia; or were growth retarded and required intensive care; or had received an exchange transfusion (mean wt 1.5 kg; 26-39 wk).On Day 1, the CA/SMA ratio in the AT RISK group was significantly higher than the PRETERM group (p<0.03); this reflected lower SMA velocities in the AT RISK group compared with controls (P<0.02 cf TERM). In the AT RISK group, abnormalities in SMA velocities and in the CA/SMA ratio were still signficantly abnormal compared with TERM controls on Day 4 (p<002). These data provide a rational explanation for the link between NEC and its known risk factors.