OBJECTIVE To investigate the prevalence of anti-endothelial cell antibodies(AECA) and its possible role in the pathogenesis of propylthiouracil (PTU) induced ANCA positive vasculitis. METHODS Sera from 11 patients with PTU induced ANCA positive vasculitis and 10 patients with PTU induced ANCA but without clinical vasculitis were studied. Soluble proteins from in vitro cultured human umbilical vein endothelial cells were used as antigens and immunoblotting technique was performed to identify the specific target antigens. RESULTS In patients with PTU induced ANCA positive vasculitis group, 10 of the 11 patients in active phase were AECA positive and 7 of the 10 patients turned to negative in remission. AECA consisted of a group of heterogeneous antibodies. In patients with ANCA positive but without vasculitis, none was AECA positive. CONCLUSION AECAs recognizing a variety of antigens could be found in sera from patients with PTU induced ANCA positive vasculitis and they had a much closer association with vasculitic disease activity compared with ANCA.