A partial cDNA clone for the Duchenne's muscular dystrophy (DMD) locus was used to investigate the expression of this locus in human muscle in vitro. Hybridization to a 14-kilobase RNA transcript was demonstrated in both fetal and mature human skeletal muscle and four lines of human muscle cells in culture. The DMD transcript was not detected in cultured cells outside the muscle lineage. In cultured muscle cells, gene expression was evident only in myotubes both before and after innervation with mouse spinal cord. Primary cultures of human myoblasts did not show the presence of the DMD transcript prior to fusion to form myotubes. An in vitro model is potentially an excellent system in which to investigate factors controlling expression of the DMD gene in normal muscle and how this expression is altered in cultured DMD muscle.