DNA was isolated and analysed in 96 patients with Duchenne or Becker muscular dystrophy (DMD, BMD); 9 of them were affected with BMD. Delections were found in 60 Patients (62.5%) using six cDNA probes. In some cases the PCR technique was also applied. In patients with BMD all deletions but one were in frame and involved exons 45-54. On the contrary, most deletions in DMD were out of frame and varied in their location. In five families prenatal diagnosis was carried out.