Activation of coagulation in acute cardioembolic stroke. The hematologic disorders in patients with acute cardioembolic stroke are not fully understood, and no reliable measures are available to identify patients at high risk for recurrent embolism. We analyzed coagulation and fibrinolytic functions in 22 patients with cardiogenic cerebral embolism less than or equal to 24 hours after onset and in 25 age-matched controls. The levels of antithrombin III, protein C, and alpha 2-plasmin inhibitor were significantly lower in the patients than in the controls (p less than 0.001, 0.02, and 0.05, respectively). In contrast, the plasma concentrations of thrombin-antithrombin III complex and crosslinked D-dimer were markedly higher in the patients than in the controls (p less than 0.01 and 0.001, respectively). At the time of admission, the plasma concentrations of thrombin-antithrombin III complex and crosslinked D-dimer in the eight patients at high risk for recurrent embolization (one with prodromal embolism, three with intracardiac thrombi, and four with recurrent embolization) were 2.8 and 3.5 times, respectively, higher than those in the 14 patients without recurrence or thrombus formation. The lowest concentration of crosslinked D-dimer in the eight patients at high risk for recurrent embolization was 600 ng/ml on admission. Our results suggest that patients with acute cardioembolic stroke have various degrees of consumption coagulopathy and that the plasma concentrations of thrombin-antithrombin III complex and crosslinked D-dimer can be useful indicators of those who are prone to recurrent embolization during this stage. 