Lactate levels in combination with lactate/pyruvate (L/P) ratio have been used to measure altered cellular redox states. We measured the cord plasma lactate levels and L/P ratios in 70 normal neonates (40 full-term and 30 preterm neonates) to set up the normal (control) ranges. The control cord plasma lactate levels and L/P ratios were 2660 [700 (SD)] micromol/l, 16 (3) in full-term neonates and 2750 (740) micromol/l, 17 (3) in preterm neonates, respectively. We also measured the lactate levels and L/P ratios in the high-risk full-term (n = 23) and preterm (n = 35) neonates, the results were 4500 (2600) micromol/l, 19 (13), and 5100 (2700) micromol/l, 26 (12), respectively. With the aid of elevated lactate levels and L/P ratios, the occurrence of neonatal encephalopathy can be predicted with a sensitivity of 100% and a specificity of 94.5% in this patient group. In our study, the six cases with abnormal neurodevelopment at 6-9 months of age all had both elevated lactate levels and L/P ratios at birth. We conclude that the measurement of lactate levels in combination with L/P ratios is a useful quantitative tool in assessing the existence and severity of perinatal hypoxia in the high-risk neonates.