The presence of antiphospholipid (aPL) antibodies has been associated with thrombosis, pregnancy loss and thrombocytopenia in the antiphospholipid syndrome (APS). The anticardiolipin and the lupus anticoagulant tests are frequently used to detect aPL antibodies. The anticardiolipin ELISA utilizes cardiolipin coated on polystyrene plates as antigen and is a very sensitive test but lacks specificity, since it can be positive in a number of infectious (such as syphilis, HIV) and autoimmune diseases other than APS. In an effort to improve specificity, new ELISA techniques that employ alternative antigens (such as β2-glycoprotein 1, particularly when coated onto oxidized microtiter plates or mixture of phospholipids) have been developed. Several investigators have reported that these new assays enable more specific determination of aPL antibodies and thus can be used more reliably for the diagnosis and confirmation of APS. This article examines the results of those studies, including data that shows correlations of these assays with clinical manifestations of APS, and proposes a new protocol for the use of laboratory tests in the diagnosis of APS.