OBJECTIVE N-acetyl-beta-D-glucosaminidase (NAG) is a lysosomal enzyme of which the activity in plasma is increased in a number of conditions including myocardial infarction. Plasma levels of cardiac proteins, such as myoglobin, troponin and creatine kinase, have been used as markers of myocardial reperfusion as well as for the prognosis of the disease. The aim of this study is to investigate whether NAG could be used as an additional biochemical marker to predict myocardial reperfusion and to find out if its release following thrombolysis has a prognostic value as well. METHOD Streptokinase (SK) in a dose of 1.5 million units was administered intravenously to 75 patients with acute myocardial infarction (AMI) and the response to SK was assessed over a period of 90 minutes. Plasma NAG activity was monitored before (0 min) and 90 min after SK treatment. RESULTS The mean NAG activity values were found to be 8.6 +/- 4.8 U/I and 10.95 +/- 7.3 U/I, respectively, and when compared using paired samples t-test revealed a significant increase (p = 0.0001) following thrombolytic therapy. The increase appears perfusion related as rabbits injected with SK failed to show any increase in plasma NAG activity. There was an association between plasma NAG activity and clinical response to SK treatment (p = 0.045). A follow-up of 66 patients over a period of 18 months, revealed increased survival in AMI patients having significantly more activity/release of plasma NAG after thrombolytic treatment (p = 0.001). CONCLUSION NAG appears to be another potential biochemical marker of reperfusion. Moreover, NAG release profile during thrombolysis could be of value in predicting prognosis of the disease.