WE describe the use of an immunoblotting technique to investigate the potential role of reaction oxygen species in the pathogenesis of Duchenne muscular dystrophy. Quadriceps femoris muscle biopsy samples were obtained from six patients with Duchenne and six with Becker muscular dystrophy, and from six control subjects. These were analysed for the presence of protein carbonyl moieties (indicative of oxidation to protein) by SDS–polyacrylamide gel electrophoresis and Western blotting, using a commercially available antibody. In all Duchenne and Becker patient samples analysed, a heavily oxidized protein species was identified migrating at 125 kDa. This oxidized species was not present (or was present at very low levels) in normal control samples. Use of the present technique also identified that the various muscle proteins in Duchenne and Becker muscular dystrophy muscle are oxidized to varying degrees, supporting the hypothesis of a differential susceptibility of proteins to oxidation in these disorders. Work from the present study further supports the hypothesis that reactive oxygen species play a role in dystrophic muscle cell pathogenesis.