Summary: Ticlopidine hydrochloride, an inhibitor of platelet aggregation that has been approved for use in the United States for secondary stroke prevention, may be more effective than aspirin for the secondary prevention of stroke, but this advantage decreases greatly over time. The pharmacology, adverse effects, efficacy, drug interactions, and indications for ticlopidine are discussed here with summaries of various clinical trials. The drug is more costly than aspirin, and patients must have complete blood counts during the first 3 months of therapy. It is recommended for those who cannot take aspirin and may be more effective in certain groups—nonwhites, diabetics, and women and those with vertebrobasilar ischemia, intermittent claudication, unstable angina, and nonproliferative retinopathy.