BACKGROUND: Unstable angina is a critical phase of ischemic heart disease, but there are no reliable noninvasive methods of assigning patients to different prognostic actegories. Recently cardiac Troponin-T has been developed as a new myocardial specific marker, especially myocardial injury. We investigated the value of the Troponin-T in unstable angina to determine whether the increase of cardiac Troponin-T might be a useful predictor of prognosis. METHODS: Unstable angina is defined as Braunwald classification(Class I, II, III). CLass I is new onset of severe angina or accelerated angina and no rest pain, class II is angina at rest but not within preceding 48 hour, and class III is angina at rest within 48 hour. We studied 16 cases of unstable angina(male:10, mean age:57+/-2year). We measured Troponin-T and CK-MB at admission, after 6 hours, and every 8 hour for 2 days. For the determination of serum Troponin-T, an enzyme immunosorbent assay (Boehringer Mannheim, ES 300 analyzer) was used. Above 0.1ng/ml was regarded as positive. During the admission, we investigated the myocardial infartion, sudden death, and the need of emergency PTCA and CABG. RESULTS: 1) Among 16 unstable angina patients, there are 12 patients in Class I(range 0.001-0.13, mean SD 0.04 0.01, median 0.02ng/ml) and 4 patients in Class III(range 0.03-1.56, mean SD 0.39 0.2, median 0.27ng/ml) and 4 patients showed positive value of Troponin-T. One was in Class I and the others were in Class III. 2) During the admission, one patient expired due to cardiogenic shock preceding inferior myocardial infarction, and 2 patients progressed non-Q wave myocardial infarction(NQMI). These 3 patients were in unstable angina Class III and had positive Troponin-T value. In Class I, one patient performed emergency CABG due to consistent chest pain at the sixth hospital day. These patient had negative Troponin-T value. 3) CK-MB increased in one patient with NQMI, and the other patients were not increased. CONCLUSION: Cardiac Troponin-T in serum appears to be a more sensitive indicator of myocardial cell injury than serum creatine Kinase MD activity, and its detection in the circulation may be a useful porgnostic indicator in patients with unstable angina.