Sex-typing of biological samples can be accomplished using the polymerase chain reaction (PCR) to amplify DNA sequences that are specific for the Y-chromosome. One such system is based on PCR amplification of the X-chromosome amelogenin gene and the amelogenin-like sequences located near the centromere of the Y-chromosome. The X and Y PCR products can be distinguished from each other on the basis of a 177 basepair (bp) insertion in the X relative to the Y. In this report, we demonstrate that the amelogenin PCR products migrate anomalously using non-denaturing polyacrylamide gel electrophoresis (ND-PAGE) as opposed to agarose gel electrophoresis or denaturing PAGE. These results may be relevant to the choice of electrophoretic system used to analyze highly polymorphic loci for individual identification.