To avoid misclassification of lowered or enhanced coagulation proteins in childhood the purpose of this study was to establish functional normal ranges for healthy children aged 6 months to 16 years. PT, aPTT, fibrinogen, antithrombin III, protein C, protein S, plasminogen and alpha 2-antiplasmin were tested using the new Automated Coagulation Laboratory (ACL) method. Values for PT, aPTT, fibrinogen, antithrombin III, plasminogen and alpha 2-antiplasmin were closely comparable in all children although we found a minimum range of 61% in children aged 8 to 16 years in plasma concentrations of alpha 2-antiplasmin. Children < 2.5 years showed reduced lower boundaries encompassing 95% of the population for protein C and protein S activity, although medians for protein S activity were similar in all children. The rapid and automatic determination of functional coagulation proteins using chromogenic substrates on the ACL 300 (25-50 microliters citrated plasma/test) renders the possibility to realize a screening program for inherited thrombotic syndromes in a routine laboratory.