Abstract： Objective To study the role of fibroblastic stromal cells in aseptic loosening.Methods Fibroblastic stromal cells were isolated from fresh pseudomembrane from 7 patients undergoing revision ar-throplasty for aseptic loosening of the hip and cultured in the presence and absence of bone cement(PMMA +BaSO_4)particles.Semiquantitive RT-PCR was performed to check the effect of bone cement particles on the expression of RANKL and TNFαmRNA in the stromal cells.The fibroblastic stromal cells were also cocultured with peripheral blood monocytes(PBMCs).At the end of the culture,immunohistochemistry staining was performed to check the expression of tartrate resistant acid phosphatase(TRAP).Resorption lacunae on dentine slices was checked using light microscopy and SEM.Results The expression of RANKL and TNfαmRNA in bone cement particles groups were increased by1.9 folds and 2.1 folds respec-tively(P=0.002,0.004 respectively),compared to the control group.TRAP positive multinuclear cells were formed on cover slips,and resorption lacunae on dentine slices was also found in the coculture group.Conclusion Fibroblastic strornal cells can respond to PMMA+BaSO_4 particles,which leads to increased expression of BANKL and TNFαmRNA.Fibroblastic stromal cells can support osteoclast formation and os-teolysis directly from PBMCs.