The Warfarin-Antiplatelet Recurrent Stroke Study is a multicenter, randomized, double-blind study comparing warfarin against aspirin in the prevention of recurrent stroke. No patient takes two active medications or two placebos. Warfarin is used in 2 mg doses sufficient to keep the international normalized ration (INR) at 1.4–2.8 while aspirin is given as 325 mg q.id. All patients are treated as if they were on true warfarin. Blood drawn at the local sites are sent to a single laboratory in the USA where the prothrombin time/INRs are determined. To maintain blinding, the values reaching the local investigator by fax are correct if the patient is truly assigned to warfarin but normal INR values for patients in the true aspirin arm are falsified by a computer program to mimic those values expected for the dose and duration of therapy had the patient actually been on warfarin. The sample size planned is > 1,900 patients, enough to detect a 30% reduction in the frequency of stroke and death in the warfarin group compared with aspirin if differences this large exist.