The aim of this study was to determine whether neutrophil activation occurs in the fetal circulation in pregnancy-induced hypertension and to correlate this with evidence of neutrophil activation in the maternal circulation. Twenty-one normal pregnancies and 23 complicated by pregnancy-induced hypertension were studied in the third trimester. The mean length of gestation at delivery was significantly shorter (P<.01) and the mean birth weight percentile was significantly lower (P<.05) in the hypertensive group; otherwise the groups were comparable. Blood was obtained before cesarean delivery or established labor in the mothers and immediately after delivery from the umbilical vein. Plasma neutrophil elastase, which is released after neutrophil activation, was measured by radioimmunoassay as a marker for neutrophil activation. The mean (± standard error) concentration of neutrophil elastase in maternal plasma in the hypertensive group (35.9 ± 4.7 ng/mL) was significantly higher than in the normal group (20.8 ± 0.87 ng/mL) (P<.005). The concentration of neutrophil elastase in umbilical venous plasma was not significantly different between the normal and hypertensive groups. However, significantly higher concentrations of neutrophil elastase were found in the umbilical venous plasma of pregnancies delivered vaginally compared with those delivered by cesarean (P<.05) regardless of diagnosis. There was no correlation between maternal venous and umbilical venous plasma neutrophil elastase concentrations, birth weight percentile, plasma urate, or platelet count. These data suggest that neutrophil activation is confined to the maternal circulation in pregnancy-induced hypertension where it may contribute to vascular damage and dysfunction in areas such as the placental bed. In addition, neutrophil activation occurs in the fetal circulation during vaginal delivery. The neutrophil activation in the fetal circulation may reflect disturbance of the placental endothelium during labor or may be a physiologic mechanism involved in parturition