In the last few years, the great progress of certain fields, such as molecular biology and development, has allowed a detailed knowledge of mechanisms implicated in cellular programing. This has permitted a rapid and unexpected advance in therapeutic cellular strategies. Thus, it has been possible to discover mechanisms involved in cellular differentiation and therefore has opened possibilities for human cellular manipulation and function replacement of damaged cells. Embryonic stem cells, have been obtained from the embryoblast. A lot of types of cellular lineages that include neurons, glial cells, pancreatic islets cells, hepatic cells, osteoblast and adipocytes, have been derived from mouse embryonic stem cells. In the same way, cellular lineages have been obtained by nuclear transference techniques capable of generating embryonic clones. Some scientist intend to evade by this approach, the bioethic reproval for human cloning, emphasizing that this is a "therapeutic cloning". In the present work, we propose to analyze mechanisms that permit stem cells to be pluripotential and discuss the ethical use of embryos as a source for stem cells with therapeutic potential.