A rapid, non-radioactive, PCR-based method to genotype the XbaI restriction fragment length polymorphism of the human factor VIII gene is described. The method uses long-distance PCR followed by XbaI restriction digestion and agarose gel electrophoresis. The 6.6 kb amplification product includes a constant XbaI site, which provides a digestion control. The specificity of the method was challenged by a blind experiment with 16 genomic DNA samples previously genotyped by Southern blot analysis: a perfect correlation was obtained between genotypes determined using Southern blot and PCR.