OBJECTIVE: To define the abnormalities of coagulation system in cerebral infarction and the effect of aspirin. BACKGROUND: Toghi et al(1990,1993) suggested that the coagulation system was enhanced at all stages of cerebral infarction and long term use of antiplatelet medication in chronic stroke patients was effective in reducing the elevated coagulant proteins level. METHOD: We determined fibrinogen, antithrombin III (ATIII), thrombin-antithrombin III complex(TAT) in plasma from 40 stroke patients - 32 acute (<7days), 18 subacute (7-30days) and 32 chronic stage (>30days), and compared 14 patients receiving aspirin from acute stage with 10 patients not receiving aspirin. RESULT: The concentrations of fibrinogen and TAT were significantly elevated in acute and subacute stages, especially in subacute stage(P<0.01), whereas AT-III was decreased only in acute stage (P<0 05). Fibrinogen levels were significantly decreased in patients receiving aspirin than in patients not receiving aspirin during subacute stage (P<0.01). CONCLUSION: These results suggest that the coagulation system is enhanced during acute and subacute stages and early use of aspirin is effective in reducing the elevated fibrinogen in subacute stage.