Polymerase chain reaction amplification and nucleotide sequencing were used to identify the molecular defect in a Japanese patient with mild hemophilia A and an alteration of a TaqI site in exon 26 of the factor VIII gene. The mutation was a G-to-T transversion in codon 2326 of the factor VIII gene resulting in an Arg-to-Leu substitution at amino acid 2307 of the protein. The mutation, which is not of the common CG-to-TG type, is at the same codon in which both nonsense and a different missense (Arg to Gln) have previously been observed.