Objective: To observe the regularity of fluctuation of tissue type plasminogen activator (t-PA) and plasminogen activator inhibitor-1 (PAI-1) in patients with acute, convalescent and chronic stages of atherosclerotic cerebral thrombosis respectively, to probe into their role in the development and prognosis of cerebral thrombosis, and into the danger of recurrence of cerebral thrombosis. Methods: T-PA and PAI-1 activities were dynamically (day 1, 3, 7, 14 and 21 after onset) determined by ELISA using Σ960 chromgenic substrate reader made in USA and corresponding development substrate inn 25 patients with acute cerebral thrombosis, and 33 patients with cerebral thrombosis during convalescent and chronic stages (> 1 month), and 38 normal controls. Results: In acute thrombotic group, the level of t-PA was the lowest on day 1, gradually increased and reached the top on day 7, then tended to decrease gradually to day 21; the PAI-1 level increased sharply and reached the top within the first 24 hrs after onset of cerebral thrombosis, decreased gradually and reached the valley on day 7, then tended to rise again. The plasma levels of t-PA and PAI-1 in patients with cerebral thrombosis were significantly lower than those of normal controls except on day 7 and 14. In patients with convalescent and sequel stages, the level of t-PA was significantly lower and that of PAI-1 was significantly higher than those of normal controls. Conclusion: The plasma fibrinolytic activity was significantly lower than normal. It suggested that the plasma t-PA and PAI-1 might play a role in the pathogenetic process of cerebral thrombosis. The thrombolytic activity in patients with cerebral thrombosis within 1 month was lower than that of normal controls. The patients with thrombosis history longer than I month were in precoagulation state, they had the danger of recurrence of cerebral thrombosis.