The dystrophin gene was analyzed in 8 Duchenne muscular dystrophy (DMD) and 10 Becker muscular dystrophy (BMD) unrelated families (22 subjects: 18 index cases and 4 sibs) for the presence of deletions by multiplex polymerase chain reaction (mPCR; 27 exons) and Southern hybridization using 8 cDMD probes. Deletions were identified in 5 DMD and 7 BMD patients (6 index cases and 1 sib). The concordance between the clinical phenotype and "reading frame hypothesis" was observed in 11/12 patients (92%). The female relatives of DMD/BMD patients with identifiable deletions were examined by quantitative mPCR. Carriers were identified in 7 families. We also describe a variation in the HindIII pattern with cDNA probe 8 and 11-14. Molecular characterization of the dystrophin gene in this study has been helpful in advising the patients concerning the inheritance of the condition, and carrier diagnosis of female relatives, and should also prove useful for prenatal diagnosis.