Bone-marrow cells have the potential to differentiate into other cell types such as muscle fibres, and can be transplanted into acutely or chronically damaged muscle as a way of delivering normal dystrophin (the protein that is defective or missing in Duchenne's muscular dystrophy) to the skeletal and heart muscle of mdx mice^,, an animal model for this disease. But the corrective potential of this approach has been hard to estimate against the high background of muscle fibres that spontaneously revert to synthesizing dystrophin, a feature of the original mdx mutation. Here we test the long-term efficacy of bone-marrow transplantation in a different mdx mutant which is free of this problem and find that it has no impact on murine muscular dystrophy.