Forty-three unrelated South Australian boys diagnosed as having either Duchenne or Becker muscular dystrophy were screened for deletions using DNA probes to the dystrophin gene. For the 35 boys with Duchenne muscular dystrophy, the deletion frequency was 43% using a simplified probing strategy based on the probes Cf56a, Cf56b, pERT87-15 and XJ (XJ1.1 or XJ2.3). The corresponding deletion frequency for the eight boys with Becker muscular dystrophy was 38%. Members of families in which these disorders result from a deletion can now choose to prevent the birth of further affected boys, using an accurate prenatal test for the specific mutation occurring within the family. Deletion analysis also has the potential to clarify the carrier status of women in these families.