Results of the use of recombinant DNA techniques for the diagnosis of both forms of X-linked muscular dystrophy, Duchenne (DMD) and Becker (BMD), over an 18 month period, are reviewed. In all, 97 families with DMD were investigated and four with BMD. In 90 families the propositi were examined for deletions, in 21 families the maximum number of meioses was examined (in order to generate recombination fraction data) and in 45 families the study was undertaken to provide carrier and prenatal diagnosis.