Bone marrow cells have multipotency for differentiation. Recently we found that type I collagen matrix induced the osteogenic differentiation of bone marrow cells. In this study we showed that TGF-beta enhanced the effect of collagen matrix on bone marrow cells and accelerated the osteogenic differentiation. These results imply that TGF-beta might play a crucial role in the osteogenic differentiation of bone marrow cells during embryogenesis and the repair of bone. (C) 1995 Academic Press, Inc.