ABSTRACTThe present study was performed in 34 patients with transient cerebral ischemia, TCI. Twenty‐four of the patients were examined angiographically. Atherosclerotic abnormalities were demonstrated in 13 and a total occlusion of the interior carotid artery was found in one patient. The angiograms were normal in 10 patients. One patient suffered from hyperlipoproteinemia, type IV, and one from diabetes mellitus. The platelet aggregation in vitro was increased significantly, as more patients than normal controls showed secondary aggregation with low ADP‐concentrations: ≤ 1 μmol (p<0.01). The fibrinolytic capacity was significantly reduced (p<0.01) but not particularly in the patients with increased tendency for platelet aggregation. No correlation found between changes in platelet aggregation, the fibrinolytic activity and the angiographic findings. The results described may favor the concept that a prophylactic use of drugs excerting an antiaggregation effect on platelets might be useful in patients suffering fr