The relation between coronary thrombolysis and coagulation variables after administration of anistreplase (anisoylated plasminogen streptokinase activator complex, APSAC) was studied in patients with an acute myocardial infarction. Fifty eight consecutive patients with acute myocardial infarction were given 30 U of anistreplase intravenously within 4 hours of the onset of symptoms. A fall in the plasma concentration fibrinogen to less than 1.0 g/l 90 minutes after administration of anistreplase was considered to reflect a systemic lytic state. Coronary angiography was performed 48 hours after thrombolytic treatment. The overall patency rate was 74% (43/58). Patency rates were significantly different in patients with a systemic lytic (83% (43/52)) and a systemic non-lytic state (0% (0/6)). The absence of a systemic lytic state after anistreplase administration seemed to be highly predictive of the failure of coronary thrombolysis. Coagulation studies showed evidence of inhibition of anistreplase induced fibrinolytic activity which may explain the failure of thrombolytic treatment in patients with evidence of a systemic non-lytic state.