From December 1976 through March 1982, 188 patients entered an open non-random study carried out on hospitalized patients with a history of transient ischemic attacks or amaurosis fugax. Ninety-two patients received peroral anticoagulants usually combined with heparin treatment during the first days of treatment, and 96 patients enteric-coated acetylsalicylic acid 0,5 g twice daily plus dipyridamole 75 mg twice daily. The patients were followed up to March 1983, irrespective of whether treatment was changed or not. Recurrent transient ischemic attack or amaurosis fugax occurred more frequently (P less than 0.01) from 2 months of follow-up and throughout the observation period in the antiplatelet-treated group. There were no statistically significant differences between the 2 groups on the originally given treatment for endpoints such as stroke (6 patients on anticoagulants, 12 patients on antiplatelet therapy) or stroke or death (11 patients on anticoagulants, 17 patients on antiplatelet therapy). The findings from this trial suggest that anticoagulant treatment is superior to antiplatelet therapy given in the prevention of ischemic attacks and that this difference mainly exists during the first one to 2 months after onset of transient ischemic attacks or amaurosis fugax.