The first aCL test was developed in 1983 and subsequently standardized. Although in the last 6 to 7 years, new and more specific tests have become available, the aCL ELISA and the LA tests are still the first choice to be used in diagnosis of APS. While there is now doubt that the anticardiolipin test is useful in the diagnosis of APS, limitations of the assay have caused uncertainty and misinterpretation of the value of the test. Utilization of validated ELISA kits with well-tested calibrators and an "in-house standard" may enable more reproducible measurements. Reporting results semiquantitatively preserves the clinical utilize of the test without the misinterpretation of a quantitative result that may lack precision. The development of newer tests such as the beta2GPI ELISA and the APhL ELISA Kit, utilizing the phospholipid mixture, give promise to a more specific and reliable diagnosis of APS, while retaining good sensitivity. Other tests such as ELISA for prothrombin antibodies and annexin V antibodies are still under development and will require standardization and extensive evaluation. The aCL test should continue to be done and included in the Sapporo criteria. The aCL test is not as specific as the anti-beta2GPI test, but it is very sensitive and together with the LA test should capture the majority of the APS patients. IgA aCL and anti-beta2GPI positivity alone is rare but occasionally found and shown to be associated with major clinical manifestations of APS. Therefore, it is now recommended to include both tests, IgA aCL and IgG, IgM and IgA anti-beta2GPI to confirm diagnosis of APS.