Antiphospholipid antibodies (APA) are a heterogeneous group of autoantibodies. Some anticardiolipin antibo- dies (ACA) are directed against epitopes expressed on b2-glycoprotein I. In 32 serum samples positive for anticardiolipin antibodies (ACA) IgG or IgM the authors examined the presence of anti-b2-glycoprotein I (anti-b2-GPI) IgG and IgM antibodies. For the examinations of antibodies the kits Anti-b2-glycoprotein I ORGenTec (Germany) ImmuLisa™ and Anti-Cardiolipin Antibody (ACA)–IgG-ACA a IgM- ACA IMMCO Diagnostics (USA/Canada) were used. The presence of both IgG antibodies was found only in 9.37% serum samples. In one IgM ACA negative sample a higher level of anti-b2-glycoprotein I was found. In 6 ACA IgM positive serum samples the presence of anti-b2-glycoprotein I was not found. Our results suggest that there may exist two different subpopulations of APA which can be differentiated by ELISA methods using different antigens.

        Key words: anticardiolipin antibodies (ACA), anti-b2-glycoprotein I (anti-b2-GPI), antiphospholipid antibodies (APA).