Stem cells are the major factor ensuring mammalian regeneration. Cell replacement therapy is an attempt to follow this natural process. Another strategy suggests a controlled de-differentiation of somatic cells to a stem-like state with subsequent re-differentiation. Indeed, the cultured mammalian somatic cells may be reprogrammed to a pluripotent state by the induction of a specific set of genes. The next logical step toward the goal of organism rejuvenation is to test the possibility of inducing the pluripotent state in somatic cells in vivo. Such an approach has the potential to improve upon and overcome several obstacles facing today's cell replacement therapy.