We have studied the response of haemostatic reaction products in peripheral blood of patients with acute ischaemic heart disease receiving combined recombinant tissue type plasminogen activator/heparin therapy. We have found evidence that formation of excessive amounts of plasmin in vivo in relation to such therapy significantly enhances the degradation of fibrin, and of fibrinogen as well as the formation of thrombin. We conclude that excessive plasmin formation by thrombolytic therapy causes systemic effects including activation of coagulation.