Antiendothelial cell antibodies (aECA) have been demonstrated in patients with systemic lupus erythematosus (SLE), but their role in the pathogenesis of this disease remains unclear. We investigated the association of aECA and anticardiolipin antibodies (aCL) with clinical and laboratory findings in patients with active SLE.Sera from 28 patients with active SLE and 22 healthy controls were assayed for IgG and IgM-aECA by cellular ELISA method using cultured human umbilical vein endothelial cells and IgG-aCL by ELISA method.Serum titers of both IgG and IgM-aECA were significantly higher in active SLE than in healthy controls. Titers of IgG-aECA were unrelated to titers of IgG-aCL. Patients with pulmonary hypertension demonstrated a marked elevation of serum titer of both IgG and IgM-aECA compared with patients without pulmonary hypertension. In addition, patients with digital vasculitis showed a significant elevation of serum titer of both IgG and IgM-aECA compared with patients without digital vasculitis. Serum titers of IgG-aECA in patients with Raynaud's phenomenon and of IgM-aECA in patients with serositis were each significantly increased compared with patients without such findings.aECA were unrelated to aCL. Serum titers of aECA are elevated in patients with active SLE, especially with pulmonary hypertension, digital vasculitis, Raynaud's phenomenon or serositis. Since pulmonary hypertension in SLE has been associated with digital vasculitis, Raynaud's phenomenon and serositis, aECA may be involved in the pathogenesis of vascular injury, leading to these manifestations.