Five hundred consecutive women (median age 33 years; range 19-45) with a history of recurrent miscarriage (median 4; range 3-16) were screened for the presence of antiphospholipid antibodies (APA)-lupus anticoagulant (LA) and/or anticardiolipin antibodies (ACA). The prevalence of persistently positive tests for LA was 9.6% and for immunoglobulin G (IgG) and immunoglobulin M (IgM) ACA was 3.3 and 2.2% respectively. Only seven women (1.4%) were LA and ACA positive. Repeat testing, after an interval of at least 8 weeks, demonstrated that only 65.7% of LA positive, 36.6% IgG ACA positive and 36.0% IgM ACA positive women on initial testing had a second positive test result. The dilute Russell's viper venom time detected the LA significantly more often than either the activated partial thromboplastin time or the kaolin clotting time (P < 0.001). There was no difference in the gestation of previous miscarriages between APA positive and APA negative women. There was no difference in the plasma beta 2-glycoprotein-I concentrations between APA positive and APA negative women with miscarriages and normal women. All women with a history of recurrent miscarriage should be tested for the presence of both LA and ACA. A second confirmatory test should be performed in those with an initial positive test result.