We report on the physical ordering of genes in a relatively small area of chromosome 19, segment q13, containing the locus for myotonic dystrophy (DM), the most frequent heritable muscular dystrophy of adulthood in man. DNAs from somatic cell hybrids with der 19q products that carry a breakpoint across the muscle-specific creatine kinase (CKMM) gene were analyzed by Southern blotting using probes for CKMM, APOC2, and the repair genes ERCC1 and ERCC2. Results were combined with data from CHEF and field inversion-gel-electrophoresis separation of large-sized DNA restriction fragments to establish a map localizing both DNA-repair genes and the CKMM gene within the same 250 kb of DNA, the order being cen-CKMM-ERCC2-ERCC1-ter, with APOC2 being at more than 260 kb proximal to CKMM. Transcriptional start sites of the CKMM and DNA-repair genes are all on the telomeric side of the genes. Our results provide a framework for the construction of a larger physical map of the area, which will facilitate the search for the DM gene.