Objective:To investigate the effect of TGF-? on osteoclast differentiation in primary murine bone marrow cell culture in the presence of receptor activator of NF-?B Ligand(RANKL) and macrophage colony stimulating facotr(M-CSF).Methods:M-CSF-dependent bone marrow cells were isolated from 5~6 weeks old mice,and cultured in the presence of RANKL at 30 ng/ml and M-CSF at 25 ng/ml with or without 1 ng/ml of TGF-? for 4 and 9 days respectively.TRAP positive multinucleated cells and resorption pits on dentine slices were counted under light microscope.Results:TRAP positive multinucleated cells were induced from murine bone marrow cell cultures with both RANKL and M-CSF,and these cells formed resorption pits on dentine slices.The number of TRAP positive multinucleated cells and resorption pits were significantly increased by 1 ng/ml of TGF-?(P