The aim of this study was to determine if there is any correlation between the hypoxia induced deterioration of renal functions and urinary excretions of endothelin (ET). Therefore using a sensitive and specific radioimmunoassay, we have investigated plasma ET-1 concentrations and urine ET-1 excretions in healthy and asphyxiated newborns. Sixteen newborns (10 boys, 6 girls) with perinatal asphyxia or hypoxia of variable seriousness which were followed at Newborn Intensive Care Unit in Eskisehir Osmangazi University Faculty of Medicine were enrolled. Simultaneously, gestation and weight matched 10 newborns (6 boys, 4 girls) with no asphyxia (first minute Apgar score >7) were enrolled as controls. Plasma ET-1 concentrations of the asphyxiated infants (61.8+/-79.3 pg/ml, between 23.4-125.2 pg/ml) were higher than in the control group (29.3+/-22.1 pg/ml, between 12.3 and 50.8 pg/ml, p<0.05). However creatinine clearance values were not different between the two groups (p>0.05), mean fractional excretion of sodium levels (FeNa%) were higher in the study group than the controls (p<0.01). Urinary ET-1 concentrations in the asphyxiated infants were 144.6+/-63.4 pg/ml versus 70.1+/-27.7 pg/ml in the control group (p<0.001). The ET clearance were more elevated in the asphyxiated newborns than in the healthy infants (p<0.05). Urinary ET-1/Cr ratio in the hypoxic infants were significantly elevated in the first day of life when compared with those of healthy infants (p<0.05). Total ET excretion was negatively correlated with FeNa (%) (r=-0.603, p<0.05). Plasma ET-1 concentrations of the asphyxiated infants reduced at 48 hours of age (p<0.001). Fifth minute Apgar score was negatively correlated with urinary ET-1 levels (r=-0.615, p<0.01), urinary Na excretion (r=-0.583, p<0.01), FeNa (%) (r=-0.597, p<0.01) and total ET excretion (r=-0.560, p<0.01) and positively correlated with ET clearance (r=0.559, p<0.05). Urinary ET-1 levels were negatively correlated with umbilical artery BE levels (r=-0.612, p<0.05). To our study, elevated urinary ET-1 levels were observed during perinatal asphyxia and urinary ET-1 levels were negatively correlated with 5th minute Apgar score and cord blood base excess levels. For this reason urinary ET-1 levels could be a marker of perinatal asphyxia as cord blood ET-1 levels. With investigations showing renal production is independent from plasma and increased urinary ET-1/Cr levels in newborn with perinatal asphyxia and also negative correlation between the total ET excretion and FeNa, urinary ET-1 levels could be served as a useful marker to detecting also impaired renal functions in infants with perinatal asphyxia.