Fibrin deposits found in the pulmonary microcirculation and in the small airways of preterm infants with severe respiratory distress syndrome (RDS) has been explained by the activation of the coagulation system and/or insufficient fibrinolysis. Previous studies suggest that disseminated intravascular coagulation is not prominent in the early stages of RDS, and there is a reduced fibrinolytic activity in these patients. The in vitro evaluation of body's fibrinolytic potential is difficult in contrast to blood clotting because fibrinolysis is only activated after coagulation. To solve this problem a standardized assay was developed to measure the global fibrinolytic capacity (GFC) in plasma. This assay allows us a sensitive and reliable parameter to evaluate the fibrinolytic potency of plasma in vitro. We therefore studied GFC in the first 6 hr after birth in preterm infants who later developed RDS. Global fibrinolytic capacity which is expressed as generated D-dimer concentrations was significantly lower in preterm infants who later developed RDS compared to the control group in this study. These findings support our previous hypothesis of "reduced fibrinolytic state in early RDS".