Antiphospholipid antibodies (APA) are autoantibodies to negatively charged phospholipids such as a cardiolipin, phosphatidylserine and phosphatidylinositol. The occurrence of APA is associated with arterial and venous thromboembolic manifestations, thrombocytopenia and recurrent fetal loss. To date most studies have concentrated on antibodies to cardiolipin specifically. In this study we present own modification of the ELISA method for assessment of antiphosphatidylinositol antibodies (API). The phosphatidylinositol isolated from small green peas was used as an antigen. To test ELISA method 151 serum samples of patients with various diseases and 22 serum samples of blood donors were examined and the results were compared with the results of anticardiolipin antibodies (ACA). The positivity of API was 22.5% and ACA 20.5% in a group of patients. The simultaneous of both types of APA was found in 15.2%.