['Ethnicity plays a role in the prevalence, isotype distribution, and clinical significance of anticardiolipin (aCL) and anti-beta2-glycoprotein I (anti-beta2-GPI) antibodies in patients with systemic lupus erythematosus (SLE). Few studies have been done in the African American population.', 'Serum samples from 100 African American patients with SLE were tested for IgG, IgM, and IgA aCL and anti-beta2-GPI antibodies by enzyme-linked immunosorbent assay (ELISA). Computerized clinical data on these patients were reviewed with a specific focus on clinical manifestations of antiphospholipid syndrome (APS).', 'Positivity for at least one isotype of aCL antibodies was found in 33% of the patients, whereas 28% were positive for at least one isotype of anti-beta2-GPI antibodies. IgA was the most prevalent isotype for both antibodies; 24% of the patients in the aCL ELISA and 19% in the anti-beta2-GPI ELISA were positive for IgA. Positivity for both aCL and anti-beta2-GPI in the same patient was seen more frequently with the IgA isotype. Fewer than half of the patients positive for aCL antibodies had medium-to-high levels of antibodies. A few patients had presented thrombotic manifestations, and these patients were positive for aCL (P = 0.01) and anti-beta2-GPI antibodies (P = 0.02). No other manifestations of APS could be significantly correlated with the presence of these antibodies.'] Are igA anticardiolipin and anti-beta2-glycoprotein I the most prevalent isotypes in African American patients with systemic lupus erythematosus?