The specific factors predisposing to thrombosis in patients with LAs have not been resolved. With extensive cross-reactivity, and several proposed sites of action, LAs and their effects may be heterogeneous. While the risk of thrombosis with phenothiazine-induced LAs is probably low, the incidence of thrombosis in association with procainamide-induced LAs is uncertain. Procainamide is a commonly used antiarrhythmic drug associated with the induction of autoantibodies, and occasionally with a lupus-like syndrome. Serologic and coagulation profile monitoring may be required to detect patients in whom LAs develop since these individuals may be at increased risk for thrombosis. Monitoring may be especially important in patients who are receiving procainamide and who have atherosclerosis and cardiac disease, since they may be at increased risk for thrombosis of coronary and other arteries. Future prospective studies are needed to investigate whether the development of lupus anticoagulants during procainamide therapy increases the risk of thrombosis.