Hemophilia A is an X-linked recessive single gene disease. If a female is a carrier, her sons have a 50% risk of being affected. Five gravidas, each with a positive family history of hemophilia A, were collected for prenatal diagnosis using DNA analysis on chorionic villi. We used two closely linked extragenic DNA markers, St14 and DX13, and three restriction enzymes, TaqI, MspI, and BglII, to study four restriction fragment length polymorphisms in the Xq28 region. From family analysis, haplotypes were constructed to track the inheritance of X-chromosomes. In family 1, the male fetus inherited the X-chromosome from his normal grandfather, thus his probability of being affected was predicted to be less than 5%. In families 2 and 3, the gravidas inherited the maternal X-chromosome with a different haplotype from that of the affected brother or nephew, thus they both have a low probability (less than 5%) of being carriers. In family 4, the gravida and her male fetus inherited the same X-chromosome as her affected brother. With coagulation assay also showing a high probability of the gravida being a carrier, the fetus was at high risk for the disease. On pregnancy termination, fetal plasma analysis confirmed the diagnosis. In family 5, the gravida's mother had homozygous haplotypes, making the distinction between two X-chromosomes impossible. Coagulation assay classified the gravida as a probable carrier.(ABSTRACT TRUNCATED AT 250 WORDS)