The complexity of the fracture repair process has been apparent to both clinicians and scientists since its first histologic description. How fracture repair is regulated, however, remains unclear. Transforming growth factor-beta (TGF-beta), one member of a class of proteins known as growth factors, may be involved in the formation of bone and cartilage. Our experimental findings implicate TGF-beta as an important regulator of cell proliferation, differentiation, and synthesis of extracellular matrix. Further elucidation of how TGF-beta regulates bone physiology is necessary to improve therapy in pathologic conditions.