The objective of this study was to examine maternal and fetal endothelin-1 (ET-1) in pregnancies complicated with intrauterine growth restriction (IUGR) and to correlate these data with umbilical artery Doppler flow velocity waveforms (FVW). Higher mean maternal (13.8 +/- 6,4 vs 9.2 +/- 3,4 pmol/L, p < 0.05) and fetal (18.5 +/- 9.6 vs 11.7 +/- 6.9 pmol/L,p < 0.05) ET-1 levels were found in pregnancies complicated with IUGR than in controls. Fetal ET- level was related to birth weight percentile for gestational week. Maternal and fetal ET-1 concentrations were not related to umbilical artery Doppler flow S/D ratio, PI and RI. Maternal or fetal ETI concentrations were also not related to umbilical artery pH, pO(2) and pCO(2). Pregnancy-induced hyperten-sion was significantly associated with an elevated fetal and maternal ET-1 concentration. In conclusion, increased production and secretion of ET-I may play a role in the pathophysiology of idiopathic IUGR. Over-production of ET-1 in IUGR is not associated with increased placental resistance as reflected in abnormal umbilical artery Doppler FVW.