The role of embryonal or adult stem cells, in particular bone marrow (BM)-derived stem cells, in regenerating the kidney after injury has been the subject of intensive investigation. BM-derived stem cells have been shown to give rise to small numbers of most renal cell types, including tubular cells, mesangial cells, podocytes, vascular cells and interstitial cells. However, the role this infrequent display of BM cell plasticity plays in organ regeneration is less certain. Injections of BM-derived cells do improve renal function in many animal models of renal disease. Current opinion attributes this renoprotective effect mainly to paracrine factors supporting regeneration by local renal cells and to immunomodulatory effects, rather than to transdifferentiation of BM cells into renal cells. Several groups have identified native renal stem cell populations, although their role in renal regeneration has not yet been well defined.