Clopidogrel bisulfate is an anti-platelet drug, that is, a drug that inhibits the ability of platelets to clump together as part of a blood clot. It is similar to ticlopidine in chemical structure and in the way it works. Unlike ticlopidine, clopidogrel bisulfate does not cause serious reductions of white cells in the blood and, therefore, routine blood testing to determine if the white blood cell count is low is not necessary during treatment. The risk of heart attacks and strokes (which usually are caused by blood clots) is increased in patients with a recent history of stroke or heart attack and patients with peripheral vascular disease. (Peripheral vascular disease is the same as atherosclerotic arterial disease or "hardening" of the arteries in which the arteries become narrowed. It frequently occurs in the legs and often causes claudication or pain in the legs upon walking). Clopidogrel bisulfate is used to reduce the risk of heart attacks and strokes in these patients.