Myoblast transplantation has been considered a potential treatment for some muscular disorders. It has proven very successful, however, only in immunodeficient or immunosuppressed mice. In this study, myoblasts from C57BL10J +/+ mice were transplanted, with no immunosuppressive treatment, in the tibialis anterior of fully histocompatible but dystrophin-deficient C57BL10J mdx/mdx mice. One to 9 months after transplantation, the success of the graft was evaluated by immunohistochemistry. All the transplanted mice (n = 24) developed dystrophin-positive fibers following transplantation. Depending on myoblast cultures, transplantations, and time of analysis, the mice presented 15 to 80% of dystrophin-positive fibers in transplanted muscles. These fibers were correctly oriented and they were either from donor or hybrid origin. The dystrophin-positive fibers remained stable up to 9 months. Possible humoral and cellular immune responses were investigated after grafting. Antibodies directed against dystrophin and/or muscle membrane were developed by 58% of the mice as demonstrated by immunohistochemistry and Western blotting. Despite the presence of these antibodies, dystrophin-positive fibers were still present in grafted muscles 9 months after transplantation. Moreover, the muscles did not show massive infiltration by CD4 cells, CD8 cells, or macrophages, as already described in myoblast allotransplantations. This lack of rejection was attributed to the sequestrated nature of dystrophin after fiber formation. These results indicate that myoblast transplantation leads to fiber formation when immunocompetent but fully histocompatible donors and recipients are used and that dystrophin incompatibility alone is not sufficient to induce an immunological rejection reaction.