Levels of beta-thromboglobulin and platelet factor 4 in 46 patients with transient ischemic attacks and the influence of treatment with dipyridamole or aspirin plus dipyridamole were evaluated. Patients not receiving therapy showed levels of beta-thromboglobulin significantly higher than controls. However, patients taking only dipyridamole showed values of beta-thromboglobulin significantly lower than untreated patients or those taking aspirin plus dipyridamole. No significant difference was observed with regard to platelet factor 4 between the patients.