A plot of cumulative informativeness of panel of markers linked to factor VIII locus used for polymorphic DNA analysis of haemophilia A in Bulgaria. By polymorphic DNA analysis of the factor VIII gene locus carrier status of females in 30 Bulgarian families out of 32 (94%) could be determined. Intron 22. and intron 13. STR dinucleotide repeats used together are informative in 64% of haemophilia A families. Adding biallelic Hind III/Bcl I RFLP polymorphic system and Xba I PFLP results in further increase in percentage of informative families up to 70%. IVS25STR marker is informative in a limited proportion of cases (increases informativeness up to 72% of the families). Intron 7. SSCA haplotype data does not add to the proportion of cases in which at least one marker is informative. St14 tandem repeat exhibits the highest heterozygocity rate of all factor VIII gene linked markers and thus proves to be the most informative marker in the Bulgarian population. St14 is a marker of choice in cases when none of the intragenic markers is informative, nevertheless, its location apart of factor VIII gene poses risk of misdiagnosis due to marker-to-gene recombination.