Objectives: To evaluate the relationship of endothelin 1 (ET-1) and leptin concentrations in women and newborns following a pregnancy complicated with intrauterine growth restriction (IUGR). Methods: Twenty-five women with a pregnancy complicated with IUGR at 19 different gestational ages were matched with women with uncomplicated pregnancies. Blood samples from the umbilical artery and maternal peripheral venous circulation were collected at delivery, and ET-1 and leptin levels were determined from the blood samples. Data relating to obstetric complications (e.g., pregnancy-induced hypertension), delivery (e.g. mode, birth weight, signs of intrapartum fetal distress, and Apgar scores) were also recorded. Results: Mean matemal ET-1 (13.4+/-6.2-9.9+/-2.9 pmol/1) and mean fetal ET-1 (14.5+/-4.2-11.7+/-3.1 pmol/1) concentrations were significantly higher when women had experienced pregnancies complicated with IUGR than when they had had normal pregnancies. Mean fetal leptin concentration was significantly lower in the study group (6.8+/-2.2 ng/ml) than in the control group (10.6+/-3.6 ng/ml (P<0.05). However, fetal leptin per kilogram of fetal weight was not significantly different in the study group (3.16+/-1.18 ng/ml) than in the control group (3.23+/-0.96 ng/ml) (P>0.05, paired t-test). However, a statistically significant correlation was observed between fetal leptin concentrations per kilogram of fetal weight and fetal endothelin concentrations in pregnancies complicated with IUGR (r=0.546; P<0.05). Conclusions: These results suggest the intertwined roles of ET-1 and leptin in the pathophysiology of IUGR. Further studies concerning interaction between these peptides in different pregnancy conditions may provide important information about the actions of ET-1 and leptin on fetal growth. (C) 2003 International Federation of Gynecology and Obstetrics. Published by Elsevier Ireland Ltd. All rights reserved.