Adult and embryonic stem cells have drawn a lot of attention in the last decade as new tools in regenerative medicine. A variety of such cells have been discovered and put forward as candidates for use in cell replacement therapy. Investigators hope that some, if not all, of our organs can be replaced or restored to function; that new livers, kidneys, and brain cells can be produced. Many reviews have already been written about stem cells and their potential use in regenerating tissues. In this study, we would like to call attention to a different application of a special group of adult stem cells, the stromal cells in the bone marrow (also called mesenchymal stem cells or MSCs). These cells have been discovered to modulate immune function. They can easily be expanded in culture and surprisingly, they also seem not to be immunogenic. Thus, they can be removed from donors, expanded, stored in freezers, and used as allogeneic transplants in a variety of diseases in everyday medicine.