In Kennedy disease (an X-linked motoneuronal disorder associated with an increase in the number of (CAG)n triplet repeats in the first exon of the Androgen receptor gene; about twice as many as in normal conditions), polymerase chain reaction-amplified genic products exhibit two DNA fragments in the heterozygous female carriers, one with a range between 468 and 495 bp in the normal polymorphic population and a fragment corresponding to the pathological state that reaches 573 bp. These fragments are easily separated by gel-slab electrophoresis and detected by intercalating dye staining (ethidium bromide). As an alternative procedure, capillary zone electrophoresis in polymer networks, consisting of 8% polyacryloylaminoethoxyethanol at 0% cross-linker, offers a simple procedure for separation and on-line detection via UV absorbance at 254 nm, thus avoiding additional staining steps. The capillary column can be repeatedly used for up to 80-100 times and the electropherogram is stored on a magnetic support. Easy comparison among different runs is obtained by aligning all tracings to an internal standard of a 650 bp fragment added as a marker.