Cells with myogenic potential are present in many tissues, and these cells readily form skeletal muscle in culture. We here focus on menstrual blood as another cell source for regenerative medicine. Menstrual blood-derived cells have high replicative ability, similar to progenitors or stem cells, and transdifferentiate or meta-differentiate into myocytes in vitro at unexpectedly high frequencies. This unique phenotype can be explained by histological and embryological aspects of the endometrium. The remarkable myogenic capability of these cells enables us to "rescue" dystrophied myocytes of the mdx model of Duchenne muscular dystrophy through cell fusion and transdifferentiation. Endometrial cells supplied as a form of menstrual blood-tissue mixture can be used for cell-based therapy in addition to a place for embryo implantation.