This is a competing renewal application for a Center to prepare adult stem/progenitor cells from the bone marrow of human volunteers and rodents, define the quality of the cells, and then distribute them to multiple investigators. The adult stem/progenitor cells we prepare were originally referred to as fibroblastic colony forming - units, then as marrow stromal cells in the hematological literature, subsequently as mesenchymal stem cells, and most recently as multipotent mesenchymal stromal cells or MSCs. Since its establishment in June of 2003, the Center has made 451 shipments of 1,013 vials of frozen MSCs to 220 individual investigators, 129 of which are NIH funded (Appendix A). An additional 41 investigators have submitted MTAs to receive MSCs; of which 14 are NIH funded. A total of 114 investigators have provided letters of support for this competing renewal application. The Specific Aims are: 1. To continue to produce standardized preparations of human MSCs (hMSCs) for distribution to other investigators. 2. To continue to provide similarly characterized preparations of rat MSCs (rMSCs) for distribution to other investigators. 3. To continue to provide similar preparations of mouse MSCs (moMSCs) for distribution to other investigators. 4. To develop improved methods for isolating and characterizing hMSCs. The need for experiments with fully characterized MSCs has become critical with the current efforts by us and others to initiate Phase I and Phase II clinical trials with MSCs.