We investigated the clinical significance of IgG phospholipid-dependent anti-beta(2)-glycoprotein I (beta(2)-GPI) antibodies in patients with SLE. The study population consisted of 140 patients with SLE. Sera were examined for IgG phospholipid-dependent anti-beta(2)-GPI antibodies by ELISA. IgG phospholipid-dependent anti-beta(2)-GPI antibodies were detected in 21 of 140 patients (15%) and remained positive from 4 to 98 months. Significantly higher incidences of thrombosis, intrauterine fetal loss, thrombocytopenia, patients with antiphospholipid syndrome (APS), prolonged APTT, BFP-STS and hemolytic anemia were found in SLE patients with phospholipid-dependent anti-beta(2)-GPI antibodies. Moreover, significantly lower incidences of malar rash and serositis were found in SLE patients with phospholipid-dependent anti-beta(2)-GPI antibodies, and the majority of these patients satisfied four or five of the revised criteria items of the American Rheumatism Association. These differences were not observed when we compared clinical manifestations in anticardiolipin antibody-positive patients with those in antibody-negative patients by conventional ELISA. These results indicated that SLE patients with IgG phospholipid-dependent anti-beta(2)-GPI antibodies show an unique form of SLE.