Dental enamel is a product of ameloblast cells, which secrete a mineralizing organic matrix, composed primarily of amelogenin proteins. The amelogenins are thought to be crucial for development of normal, highly mineralized enamel. The X-chromosomal amelogenin gene is a candidate gene for those cases of amelogenesis imperfecta, resulting in defective enamel, in which inheritance is X-linked. In this report, a kindred is described that has a C to A mutation resulting in a pro to thr change in exon 6 of the X-chromosomal amelogenin gene in three affected individuals, a change not found in unaffected members of the kindred. The proline that is changed by the mutation is conserved in amelogenin genes from all species examined to date.