Serum leptin, the product of the obesity (ob) gene, correlates with adiposity and increases fat utilization. Leptin mRNA is present in the placenta, suggesting a role for leptin in fetal growth. Maternal serum leptin, triglyceride (trig) and free fatty acids (FFA) are elevated in healthy pregnancy, and are increased further in preeclampsia (PRE). Umbilical cord leptin levels correlate with birth weight, but not with maternal leptin levels in healthy pregnancy. Preeclampsia is associated with reduced perfusion of the placenta. We hypothesized that leptin production is increased in poorly perfused placenta in PRE and by increasing maternal fat utilization increases fuel availability to the fetus promoting fetal growth. Methods: Venous blood was obtained prepartum from 14 women with PRE and 15 healthy pregnant women (CNTL). Mixed arterio-venous blood was obtained from the umbilical cord of their infants at delivery. Plasma leptin concentration was measured by human antibody RIA. Lipids were measured by standard techniques. Data were analyzed using Mann-Whitney comparison of medians and Pearson correlation. Results: Median gestational age (38.1 v 37.7 wks), birth weight (BW, 3.1 v 3.2 kg), maternal leptin (52.8 v 26.7 ng/ml), cord leptin (3.7 v 5.6 ng/ml), maternal trig (263 v 239 mg/dl) and FFA (0.84 v 0.61 mmol/L) did not differ between PRE and CNTL, while BW%ile (29.3 v 59.7%) was significantly different at p=0.05. The correlation between maternal and cord leptin was highly significant in PRE (r=0.87, p=0.000) but not in CNTL(r=-0.16). Maternal trig did not correlate with leptin in PRE (r=-0.34) or CNTL (r=0.10). Maternal FFA correlated with leptin in CNTL (r=-0.72, p=0.003) but not PRE (r=-0.16). BW correlated with both maternal leptin (r=0.71, p=0.004) and cord leptin (r=0.67, p=0.012) in PRE. Only cord leptin was related to BW in CNTL (r=0.69, p=0.005). Conclusion: These data confirm the positive relationship between cord leptin and BW. We also found highly significant correlations of maternal leptin to cord leptin and to BW in preeclampsia which are not present in healthy pregnancy. Our hypothesis that maternal leptin increased in preeclampsia to increase fuel availability for the fetus is, however, not supported by these preliminary data.