In the adult male, germ cell differentiation takes place in the seminiferous tubules of the testis by a complex, highly organized and very efficient process. A population of diploid stem-cell spermatogonia that lie on the basement membrane of the tubule continuously undergoes self-renewal and produces progeny cells, which initiate the process of cellular differentiation to generate mature spermatozoa. Each testis contains many seminiferous tubules, which are connected at both ends to a collecting system called the rete testis. The mature spermatozoa pass from the tubules into the rete and are then carried through efferent ducts to the epididymis for final maturation before they are ready to fertilize an egg. In previous studies, we have demonstrated that donor testis cells collected from a fertile mouse are able to generate spermatogenesis when transplanted to the seminiferous tubules of an infertile male. The spermatozoa produced by the recipient from the donor-derived spermatogonial stem cells are able to fertilize eggs and produce progeny carrying the donor male haplotype. Furthermore, donor testis stem cells from a rat will generate normal rat spermatozoa following transplantation to a mouse testis. The spermatogonial transplantation technique is clearly valuable and applicable to many species, but it is difficult. Therefore, several procedures to introduce donor cells into the seminiferous tubules of a recipient have been developed using the mouse as a model, and they are described here in detail. The results indicate that microinjection of cell suspensions into the seminiferous tubules, efferent ducts or rete testis are equally effective in generating donor cell-derived spermatogenesis in recipients. Each approach is likely to be useful for different experimental purposes in a variety of species.