The clinical value of IgG and IgM cardiolipin antibodies (CLa) was examined in 22 patients with myocardial infarction and 9 patients with unstable angina (UA). Higher IgG levels were observed in 41% of MI patients and 55% of UA patients. There was a significant correlation between the detection of IgG CLa in patients with a history of myocardial infarction and the presence of left ventricular intracavitary thrombosis. The levels of IgG CLa were increased in 78% of patients with history of MI and in 32% without MI history. In addition, those of IgG CLa was higher in 80% of IM patients with signs of intracavitary thrombosis and in 38% with cavitary thrombosis. The findings suggest that antibodies to cardiolipin (of IgG in particular) make contribution to the development of thrombotic events in patients with coronary atherosclerosis in the absence of autoimmune pathology.