To determine whether they could establish reliable, objective criteria that would predict safe, primary closure of abdominal wall defects (omphalocele/gastroschisis) in newborn infants, the authors measured intraoperative changes in intra-gastric pressure (IGP), central venous pressure (CVP), cardiac index (CI), systolic arterial blood pressure (BP), and heart rate (HR). Eleven neonates, who averaged 2.7 kg (range 1.5-4.1 kg) and 36 weeks gestation (range 30-41 weeks) were anesthetized with fentanyl (7.5-12.5 micrograms/kg), metocurine (0.3 mg/kg), and oxygen. Three infants had defects that were too large to close primarily. Of the eight infants who underwent primary closure, four required re-operation within 24 h because of oliguria or poor peripheral perfusion. Infants who required re-operation had intra-gastric pressures of 20 mmHg or more, a decrease in CI of 0.78 1.min.m2 or more, and an increase in CVP of 4 mmHg or more. Heart rate, BP, and systemic vascular resistance did not differ in infants requiring and not requiring re-operation. The authors conclude that intraoperative measurement of changes in IGP, CVP, and/or CI can reliably predict success or failure of primary operative repair of abdominal wall defects in human neonates.