Plasma lactate concentrations have been used as an indicator of tissue hypoxia and as a predictor of the outcome of critical illness in adults. We evaluated the value of plasma lactate levels in predicting death in neonates with severe hypoxemia requiring extracorporeal membrane oxygenation (ECMO). We retrospectively reviewed the medical records in regard to plasma lactate levels and other clinical and biochemical measurements in 28 consecutive neonates requiring ECMO from July 1992 to December 1993. Seven infants died (mortality rate, 25%); 21 infants were short-term survivors and 20 infants were discharged from the unit. The plasma lactate values for survivors and nonsurvivors, respectively, were 10.0 +/- 6.35 mmol/L vs 24.9 +/- 9.90 mmol/L on admission, and 13.7 +/- 6.32 mmol/L vs 38.4 +/- 9.20 mmol/L at peak (both p < 0.00001). The survivors had a significant decrease in plasma lactate levels 12 hours after the start of ECMO: the nonsurvivors had persistent, severe hyperlactatemia. Apart from being less acidotic, the survivors did not differ from the nonsurvivors in other clinical and biochemical measurements. An admission plasma lactate concentration of < 25 mmol/L predicted survival with a sensitivity 100%, a specificity 71.4%, and positive and negative predictive values of 91.3% and 100%, respectively. We conclude that plasma lactate levels could be useful in predicting death in neonates with severe hypoxemia requiring ECMO. Further prospective evaluations of the predictive value of plasma lactate levels in sick neonates are required to confirm these initial observations.