Genes of three protein families, which are in part specifically expressed in the course of terminal differentiation of human epidermis, have previously been mapped to chromosome 1q21. Here we show that these genes are physically linked within 2.05 Mb of DNA. The order is calpactin I light chain, trichohyalin, profilaggrin, involucrin/small proline-rich protein, loricrin, and calcyclin. The colocalization in the 1q21 region together with their functional interdependence during epidermal differentiation raises the question whether these genes share regulatory elements which control their transcriptional activities. As several of them are potential candidate genes for dyskeratotic skin diseases, this physical map should be of great value for genetic linkage analyses.