Osteogenic growth polypeptides regulate bone cell function in vitro and may act in vivo in an autocrine, paracrine, or endocrine manner. Several of these polypeptides are present in the blood in an inactive form. During postablation bone marrow regeneration these factors may be activated, released from the blood clot, and together with locally produced polypeptides mediate the initial intramedullary/systemic osteogenic phase of this process. Then, the same and/or other polypeptides expressed by stromal cells have the potential to promote the second phase of regeneration that consists of osteoclastogenesis, resorption of the transient intramedullary bone, and hemopoiesis. This may be an indirect influence since these polypeptides can regulate the stromal cell expression of some of the hemopoietic factors. Clinically, the osteogenic growth polypeptides that regulate osteogenesis and hemopoiesis have a potential role in osteoporosis therapy, implant bone surgery, and bone marrow transplantation. © 1994 Wiley-Liss, Inc.