Abstract: Plasma activities of t-Pa and PAI were measured in 21 patients with AMI. Compa-red with the control group（16 cases）. the activity of t-Pa was markedly decreasd and that of PAI significantly elevated （P＜0.01 and 0.001 respectively）shortly after the onset of AMI· Butboth retuned to normal range during the convalescent stage, Our results indicate that change ofplasma t-Pa and PAI may play an important role in the pathogenesis of AMI.