Summary. Background: Earlier studies found strong support for a genetic basis for regulation of coagulation factor levels and measures of a prethrombotic state (d-dimer, prothrombin fragment 1.2). Objectives: Estimation of how much of the variation in the levels of coagulation factors and measures of a prethrombotic state, including measures of protein C activation and inactivation, could be attributed to heritability and household effect. Patients and methods: Blood samples were collected from 330 members of a large kindred of French-Canadian origin with type I protein C deficiency. Heritability and common household effect were estimated for plasma concentrations of prothrombin, factor (F)V, factor VIII, factor (F)IX, fibrinogen, von Willebrand factor (VWF), antithrombin, protein C, protein S, protein Z, protein Z-dependent protease inhibitor (ZPI), fibrinopeptide A (FPA), protein C activation peptide (PCP), activated protein C–protein C inhibitor complex (APC–PCI), activated protein C–α1-antitrypsin complex (APC–α1AT), prothrombin fragment 1.2 (F1.2) and d-dimer, using the variance component method in sequential oligo-genic linkage analysis routines (SOLAR). Results: The highest heritability was found for measures of thrombin activity (PCP and FPA). High estimates were also found for prothrombin, FV, FIX, protein C, protein Z, ZPI, APC–PCI and APC–α1AT. An important influence of shared household effect on phenotypic variation was found for VWF, antithrombin, protein S and F1.2. Conclusions: We found strong evidence for the heritability of single coagulation factors and measures of a prethrombotic state. Hemostatic markers with statistically significant heritability constitute potential targets for the identification of novel genes involved in the control of quantitative trait loci.