Current progress in adenoviral (Ad) gene therapy for Duchenne muscular dystrophy (DMD), a degenerative, inherited neuromuscular disease characterized by a lack of a functional dystrophin protein, has revealed many physical and biochemical obstacles affecting the transduction of muscle. To avoid barriers such as the basal lamina surrounding each muscle fiber and a mature immune system, fetal gene therapy could be an attractive method to deliver therapeutic genes to afflicted individuals. The ability to use a small vector load to transduce target organs in utero, combined with the possibility of transducing progenitor or stem cells, provides a key advantage over post-natal treatment. High-capacity Ad (HC-Ad) vectors devoid of all viral genes have shown more persistent expression after transduction in utero, as compared to first-generation Ad vectors, and have the added ability to carry the full-length 14 kb murine or human dystrophin cDNA. In a previous transduction study in C57BL/6 mice in utero, transgene expression was stable for at least 5 months by intramuscular injection. Furthermore, a lack of neutralizing antibody response to the Ad vector in injected animals was observed, which may allow for repeat administration of vector later in life. For this study we wanted to determine if a single intramuscular in utero injection of an HC-Ad vector carrying the full-length murine dystrophin cDNA could ameliorate the dystrophic phenotype, restore the dystrophin-glycoprotein complex, and provide functional correction of transduced muscles in the mdx mouse, an animal model for DMD. Using a surgical approach on pregnant mdx mice carrying embryonic gestation day 16 fetuses (E-16), one hind limb of fetal mice was injected with an HC-Ad vector carrying dystrophin. The injected pups were delivered naturally and analyzed at 9 weeks of age. In vitro physiological studies showed modest functional correction as assessed by specific tetanic force and muscle weight in an in utero transduced tibialis anterior muscle demonstrating recombinant dystrophin expression. Furthermore, the dystrophin-glycoprotein complex was restored in those fibers expressing dystrophin. These studies provide the first evidence that dystrophin gene delivery in utero has the potential for therapeutic effect in DMD.