BACKGROUND: Early diagnosis and treatment of acute coronary syndrome(ACS) encompassing acute myocardial infarction(AMI) and unstable angina(UA) is very important. Cardiac troponin T(cTnT) is known to be more specific to myocardium, and the level increases early and persistently during the period of 7 to 14 days after the onset of symptoms. The aim of this study was to evaluate the usefulness of cTnT for the diagnosis of ACS comparing with other biochemical markers. METHODS: The precision, linearity, lower limit of detection and interferences for cTnT by electrochemiluminescence were evaluated. cTnT and other conventional cardiac markers were determined for 128 AMI, 96 UA and 72 stable angina(SA) patients. The medical records of these patients were reviewed. RESULTS: cTnT-positive rates in AMI patients were 87.5-100% in all periods. cTnT positive rate was maintained as 100% from 3 hours to 96 hours after heart attack. Although CK-MB positive rate was as high as 85.7% at 6 hours, it decreased after 61 hours. The positive rate of LD and LD isoenzyme were very low(33.8-75%). In UA patients, mean positive rates of cTnT and CK-MB were 22.6% and 22.9% respectively. For the diagnosis of ACS comparing with SA, the sensitivity and specificity of cTnT were 63% and 94%(cut-off, 0.1 microgram/ml), meanwhile these of CK-MB were 53% and 90%, respectively(cut-off, 5 microgram/ml). CONCLUSIONS: cTnT was more useful and sensitive than CK-MB, LD, or LD isoenzyme. ACS also could be diagnosed with cTnT and CK-MB with sufficiently high specificity. cTnT seemed to be slightly more specific than CK-MB for the diagnosis of ACS.