Dystrophin and its gene were studied in a patient with McLeod syndrome. This X-linked recessive myopathy has been localized to Xp21, as has the Duchenne muscular dystrophy gene locus, which codes for dystrophin. Histopathological study of the patient's muscle showed mild subclinical myopathy. Immunological studies of dystrophin in two separate biopsy specimens and analysis of dystrophin gene DNA from a blood sample did not detect an abnormality. This suggests that the Duchenne muscular dystrophy gene, albeit close to the McLeod locus, is not involved in McLeod myopathy.