Accumulating evidence demonstrates that adult tissues contain a population of very pluripotent stem cells and recently our group identified a population of very small stem cells in murine bone marrow and other adult organs that express several markers characteristic for epiblast/germ line-derived cells. We named these rare cells "very small embryonic/epiblast like stem cells (VSELs)'. We hypothesized that these cells, which are deposited during early gastrulation in developing tissues/organs, play an important role in the turnover of tissue-specific/committed stem cells.