Sixty probable carriers of haemophilia from 25 families were studied by using coagulation phenotype and DNA analysis: 33 with haemophilia A and 27 with haemophilia B. Coagulation phenotype was based on factor VIII/IX assay and DNA analysis on the examination of restriction fragment length polymorphisms (RFLPs) within and closely linked to factor VIII or IX: 3 RFLP for factor VIII and 3 for factor IX. The comparison between the coagulation phenotype and RFLP analysis showed the misclassification of 15 females (6 for haemophilia A and 9 for haemophilia B). Four prenatal haemophilia A diagnosis were made by DNA analysis of chorionic villi, taken with a transcervical trophoblastic biopsy, between the 18th and the 11th week.