The plasma levels of ET-1, TXB₂(a stable metabolite of TXA₂) and 6-K-PGF_1α(a stable metabolite of PGI₂) in 24 postasphyxia newborns(9 cases complicated respiratory failure) and 33normal neonates were determined by the RIA method. The results showed that birth stress,especially asphyxia may contribute to the enhancement of fetal circulating ET-1, TXA₂ and PGI₂ levels. The concentrations of ET-1,TXA₂ and PGI₂ declined with the improvement of oxygenation.There were a homeostasis between ET-1 and PGI₂, TXA, and PGI₂. The plasma ET-1 levels were positively correlated with the severity of the respiratory failure. The result indicated that ET-1 could play an important role in hypoxic pulmonary vascular contraction.