STRO-1 is a cell surface antigen expressed by stromal elements in human bone marrow, identified by monoclonal antibody STRO-1. Approximately 10% of mononuclear cells, greater than 95% of which are nucleated erythroid precursors, are STRO-1 positive, whereas the CFU-GM (colony-forming unit granulocyte-macrophage), BFU-E (erythroid burst) and CFU-Mix (mixed colonies) committed progenitor cells are negative. CFU-F (fibroblast colony-forming cells) are present exclusively in the STRO-1 positive population. When plated under long-term bone marrow culture conditions, STRO-1 positive cells generate adherent cell layers containing multiple stromal cell types, including adipocytes, smooth muscle cells, osteoblasts, chondrocytes, and fibroblastic elements. In combination with glycophorin A, STRO-1 is a useful marker for identification of mesenchymal stem cells. STRO-1 and CD117 are markers for osteosarcoma cells.