Utrophin is highly homologous and structurally similar to dystrophin, and in gene delivery experiments in mdx mice was able to functionally replace dystrophin. We performed mini-utrophin gene transfer in Golden Retriever dogs with canine muscular dystrophy (CXMD). Unlike the mouse model, the clinicopathological phenotype of CXMD is similar to that of Duchenne muscular dystrophy (DMD). We injected an adenoviral vector expressing a synthetic utrophin into tibialis anterior muscles of newborn dogs affected with CXMD and examined transgene expression by RNA and protein analysis at 10, 30 and 60 days postinjection in cyclosporin-treated and -untreated animals. Immunosuppression by cyclosporin was required to mitigate the immune response to viral and transgene antigens. RT-PCR analysis showed the presence of the exogenous transcript in the muscle of cyclosporin-treated and -untreated animals. The transgenic utrophin was efficiently expressed at the extrajunctional membrane in immunosuppressed dogs and this expression was stable for at least 60 days. We found reduced fibrosis and increased expression of dystrophin-associated proteins (DAPs) in association with muscle areas expressing the utrophin minigene, indicating that mini-utrophin can functionally compensate for lack of dystrophin in injected muscles. For this reason, utrophin transfer to dystrophin-deficient muscle appears as a promising therapeutic approach to DMD.