Duchenne muscular dystrophy (DMD) is a severe, progressive muscle-wasting disease that causes cardiac or respiratory failure and results in death at about 20 years of age. Replacement of the missing protein, dystrophin, using myoblast transfer in humans or viral/liposomal delivery in the mouse DMD model is inefficient and short-lived. One alternative approach to treatment would be to upregulate the closely related protein, utrophin, which might be able to compensate for the dystrophin deficiency in all relevant muscles. As a first step to this approach, we have expressed a utrophin transgene at high levels in the dystrophin-deficient mdx mouse. Our results indicate that high expression of the utrophin transgene in skeletal and diaphragm muscle can markedly reduce the dystrophic pathology. These data suggest that systemic upregulation of utrophin in DMD patients may lead to the development of an effective treatment for this devastating disorder.