The clinical and serological findings in 13 patients with myocardial infarction and antiphospholipid antibodies (the 'lupus anticoagulant', antibodies to cardiolipin, antibodies to phosphatidylethanolamine (one patient] seen by our unit and other units from 1984 to 1989, are presented (eight males and five females, ages ranging from 20 to 52 years). Five suffered myocardial infarction before the age of 30; four of these five were in their early 20s. Other risk factors such as excessive smoking (greater than 20 cigarettes a day) (two patients), long-term treatment with steroid (one) and use of oral contraceptives (one) were present. One patient had demonstrated a plasminogen activator deficiency and one a deficiency of protein C. Two patients developed myocardial infarction six to eight weeks after warfarin was discontinued for recurrent deep vein thrombosis. Six patients had SLE as defined by the revised 1982 criteria, three suffered from 'lupus-like' disease, while four patients conformed to a 'primary' antiphospholipid syndrome.