Objective To investigate the expressions and role of bone morphogenetic protein(BMP) 2,basic fibroblast growth factor(bFGF),Core-binding factor al(Cbfa1)in the process of pathological bone formation in ankylosing spondylitis.Methods The expressions of BMP-2,bFGF and Cbfa1 in the synovial tissues of AS patients'sacroiliac ioint were detected using in situ hybridization.They were compared with those of patients with hip replacement and the gray scale of cells was analyzed with image analysis.Results The positive expressions of BMP-2,bFGF and Cbfal in the synovial tissues of patients'sacroiliac joint with AS were stronger than those of the control group(P＜0.01).Conclusion BMP-2,bFGF and Cbfal are important factors in the process of pathological bone formation in patients with AS.They areclosely correlated with the process of bone formation in patients'sacroiliac ioint with AS.Reduction of the expressions of BMP-2,bFGF and Cbfa1 with AS can block the process of pathological bone formation.