In the west of Scotland use of a single intragenic restriction fragment length polymorphism (F9(VIII)/TaqI) allowed definitive genetic counselling for 45% of females at risk of being carriers for haemophilia B. Two further intragenic RFLPs, F9(VIII)/XmnI) and F9(VIII)/DdeI, have been applied to this population and by using all three polymorphisms the carrier status could be determined in 68% of females at risk. Linkage disequilibrium was apparent between these three RFLPs, and in the west of Scotland the single most clinically useful polymorphism was F9(VIII)/TaqI followed by F9(VIII)/DdeI and then F9(VIII)/XmnI. Overall, prenatal diagnosis by DNA analysis could be offered to 31 of 37 (84%) carriers (obligate and detected) in these families.