Stem cells have been identified and isolated in many adult tissues. They exhibit a great plasticity and the ability to give rise to differentiated cells of several lineages. The possibility of transplantation of these stem cells into an adult to develop, integrate and rebuild destroyed tissues or organs has encouraged the study of the mechanisms of the differentiation of stem cells. These cells are nowadays being called a panacea in numerous diseases and, although their functional role is not well known, they are present in several areas of the human therapy, increasing the clinical applications. They represent the future of the transplant in medicine, and open, moreover, new perspectives in the treatment of diseases, as it is the case of the regenerative medicine. Here we review the current literature examining several aspect of medical therapy such as the applicability of experimental models to clinical practice.