Recently we have available immunologic techniques with high sensitivity (nanogram 10(-9) g) useful for recognizing antibodies, including the antiphospholipid antibodies. As a consequence, a clinical syndrome termed precisely antiphospholipid or anticardiolipin syndrome was described in 1983. This clinical entity has manifestations pertaining to several medical fields such as cardiology, angiology, neurology, obstetrics and rheumatology. It is necessary to set limits for the information provided by such tests in each laboratory. In our hands the positive predictive value is very low for establishing a diagnosis of autoimmune disease. It is better as a negative predictive value to exclude that possibility. However, as is the case in almost all data generated through biological assays, a result of anticardiolipin antibody detection by ELISA is meaningful only in a clinical context. This fact is emphasized, making the point of the necessity of prospective controlled studies.