Haemophilia A, haemophilia B and von Willebrand's disease are the three commonest inherited disorders of coagulation. Genetic counselling at the time this project was undertaken (1985/86) was hampered by the inability of coagulation tests to clearly distinguish carriers from non-carriers for the X-linked haemophilias and by the need for second trimester fetal blood sampling in those families who opted for prenatal diagnosis. The present project aimed to utilise the newly available gene probes for these three conditions to measure their clinical value for improved genetic counselling within affected families.