Spermatogonial stem cells (SSCs) are located in the basal region of the seminiferous tubules and provide a self-renewing reservoir from which progenitor spermatogonia arise and transiently amplify in number before transition to a differentiating state. SSC transplantation involves grafting mouse testicular cells into the seminiferous tubules of an aspermic recipient testis that is generated either by chemical (e.g., busulfan) treatment or genetic mutations.