Hypoxanthine levels were determined in both venous and arterial cord blood of 42 neonates. Two methods were compared, a PO2 electrode determination and an HPLC (high-pressure liquid chromatography) method. A good correlation was found between the two methods. However, the HPLC method was more sensitive, more reproducible and easier to perform. Hypoxanthine levels in the umbilical artery were found to be higher than in the vein. A significant negative correlation between pH and hypoxanthine level was established. The studies showed that plasma hypoxanthine levels by themselves did not provide an absolute diagnosis of intrauterine hypoxia.