During routine testing of 5,534 reference samples from Polish Caucasian males, 1 sample showed no amplification of the X homologue of the amelogenin locus. Typing of this sample with ProfilerPlus and PowerPlex 16 yielded the same result as was observed for the SGMPlus kit. The male sample that showed no amplification of the X homologue was additionally typed with different amelogenin primers as described by Sullivan et al. and yielded only a Y homologue. Application of alternative external primers that encompassed the initial amplicons gave X-chromosome specific products. These results suggest that a lack of amplification signal with amelogenin primers present in SGMPlus, ProfilerPlus, and PowerPlex 16 kits could be due to a mutation in a primer-binding region. In testing this hypothesis, sequencing of the X fragment was undertaken with primer external to the original amplicons. A mutation was found at the most 3' base of the commonly used amelogenin reverse primer, totally inhibiting X homologue amplification with SGMPlus, ProfilerPlus, and PowerPlex kits. This occurrence was rare and should be called a mutation rather than a polymorphism, since it was found in only 1 out of 5,534 individuals, giving an allele frequency of 0.02 percent. The authors indicate they do not know of any report of this mutation and failure to amplify the X homologue of the amelogenin gene for the European population. 3 figures and 11 references