[Stem cells in medicine].

We witness an unprecedented explosion of knowledge and interest in the field of stem cells and stem cell-dependent organ systems. The notion of stem cell has expanded to encompass cells with different properties but all amenable to ex vivo manipulation. We have learned that not only rapidly self-renewing tissues, but also unsuspected systems such as the central nervous system are associated with post-natal progenitor cells. The bone marrow seems to represent an important cross-road of many different progenitors, and perhaps the easiest source of diverse progenitors to be used for therapeutic purposes in a large spectrum of diseases. While some applicative uses of post-natal progenitor cells are either already in use, or soon to be routinely implemented, much larger perspectives are linked to the design of appropriate strategies for cell delivery and stable cell transduction. Meanwhile, major gains in understanding of the biology of different diseases are implied by the very recognition that many diseases are indeed stem cell diseases.