Protein C (PC) is a vitamin K-dependent serine protease which functions as the central regulatory protein with both anticoagulant and profibrinolytic properties. The PC levels in healthy term newborns are approximately one third of adult levels. Severely decreased levels of PC are seen in sick term and preterm infants. These neonates appear to have an increased incidence of thrombosis. Undetectable levels of PC are found in homozygous PC deficient infants with DIC and purpura fulminans symptoms. In this present study we report the composition and distribution of PC in term newborn and compare the results with adult values. Plasma was obtained from placental cord blood of 20 healthy term (38-42 weeks gestation) infants. PC was immunopurified, run on SDS-PAGE, and immuno-blotted. The composition of the PC molecule in neonatal plasma is identical to that seen in adults. Using densitometry to determine the distribution of the PC components, we observed a 2-fold increase in single chain PC in the neonate as compared to the adult. In the neonate, there was an inverse correlation between the level of total PC antigen and the amount of single chain. These findings suggest the possibility that the processing of PC may be developmentally influenced.