A fragment that contains a (CA)n sequence from the 3' untranslated region of the dystrophin gene can be amplified by the polymerase chain reaction and shows length polymorphism in a Caucasian population. The two common alleles differ by 4bp. This new genetic marker has a heterozygosity of about 35% and is typed more rapidly than a conventional restriction fragment length polymorphism. Its localisation at the 3' end of the dystrophin gene makes it a useful tool for diagnostic applications in families with Duchenne/Becker muscular dystrophy, and for the analysis of intragenic recombination.