In 7 families at risk for hemophilia A 42 individuals were evaluated by the Taq I polymorphism of the extragenic probe St 14.1 and the Bcl I as well the Hind III polymorphism of the intragenic probe F8e16-19. 15 out of 20 females of the core families were identified as carriers, under them all of the obligate heterozygotes. 5 individuals were excluded as carriers. The heterozygosity for each of the RFLPs was found to be between 30% and 79%. Combining the single data in 96% heterozygosity was found under the individuals tested. A linkage disequilibrium was found between the Bcl I and Hind III polymorphismus of the probe F8e16-19. A family at risk for hemophilia B including 5 individuals was studied using the Taq I and Xmn I polymorphisms of the probe P1. In one of two females the carrier state could be excluded in the other one confirmed.