Althought there are controversies regarding the appropriate dosage and the best monitoring method, heparin is the most widely used anticoagulant. Recent reports indicate that continuous infusion appears safer and is as effective as interrnittent intravenous infusion in. thromboembolic diseases. The therapeutic arnount has been determinated on the assumption of lowest of thrombosis and bleeding. However, several studies indicate that standardized doses of heparin can induce unpredictable anticoagulation in some patients. Recently, a new method for measuring the plamsma heparin concentratiOn using a chromogenic substrate is available. We designed this study to evaluate the accuracy of aPTT in the monitoring of heparin therapy and define the appropriate dosage and rnethods for infusion in patients with acute cerebral infarction. Among the patients with acute cerebral infarction and admitted to neurology department from June 1989 to December 1989. 13 patients were enrolled. They were divided into two groups according to the heparin dosage and using bolus infusion or not. Group 1 included 6 patients(4 men, 2 women) treated with 5,000 unit bolus IV followed by contionus infusion of 15.000 unit./day. Group 2 included 7 pa tients(5 men. 2 women) treated with contionus infusion of 10.000 unit/day. Their mean age were 55.2 and 60.1 years oId respectivelv. We measured the baseline plasma heparin level. aPTT, antithrombin-III and platelet and 1 24 48 96 and 120 hours after starting therapy. The mean of the aPTT and heparin concentration of 1, 24 hour after infusion of the group 1 increased markedly near to the 3 times of control value. But the all value of the group 2 remained constratly in therapeutic range during the study. The best method of heparin administration to maintain an effective therapeutic range is continous intravenous infusion. The results of this study indicate that treatment of acute cerebral infarction with continous intravenous infusion of 10000 unit/day of heparin is more effective and safer than bol.