Duchenne and Becker muscular dystrophy are caused by defects in dystrophin synthesis. Using affinity-purified polyclonal anti-dystrophin antibodies, we have studied immunohistochemically the subcellular localization of dystrophin in embryonic, fetal, and adult human skeletal muscle. In the embryonic stages dystrophin first appears in the sarcoplasm at the peripheral ends of the myotubes, immediately adjacent to the tendons, whereas in fetal stages dystrophin is found throughout the entire myofibers. In agreement with literature data, in adult muscle dystrophin expression was found to be restricted to the sarcolemma. The sarcoplasmic localization in embryonic and fetal tissue and the sarcolemmal localization of dystrophin in mature muscle suggests the accumulation of dystrophin in the cytoplasm prior to its integration into the membrane. These results increase our knowledge of the ontogenesis of dystrophin and may lead to a better understanding of the great diversity in pathological cases of Duchenne and Becker muscular dystrophy.