Cardiac troponin-I (cTn-I) is a sensitive and specific marker for the diagnosis of acute myocardial infarction (AMI). However, elevation of serum cTn-I has been observed in some unstable angina patients who have a worse prognosis than those with normal serum cTn-I levels. It is unknown whether serum cTn-I can elevate in stable angina patients with acute ischemic burden. Therefore, the purpose of this study was to determine a serial change of cTn-I in patients with acute ischemia induced by a treadmill exercise test. Thirty-five patients suspected of having coronary artery disease and five healthy medical students were enrolled into this study. Every patient received a treadmill exercise test. Cardiac troponin-I was measured by fluorescent immunoassay before the treadmill test and at 5 minutes, 1 hour, 3 hours, and 6 hours after the treadmill test. Patients with cTn-I levels of less than 0.5 ng/ml were considered normal, and those with cTn-I levels of greater than 2.0 ng/ml was considered to have AMI. The exercise test was positive in 19 of the 35 patients and negative in 16 of the 35 patients and 5 medical students. Among the 19 patients with positive treadmill exercise test, the cTn-I concentrations were abnormally increased in 7/19 (37%) patients (mean: 1.1 +/- 0.4 ng/ml; range: 0.5 to 2.0 ng/ml). One of the 16 patients with negative treadmill test showed an increase of serum cTn-I. Normal cTn-I levels were found in the other 15 patients and the 5 medical students. In conclusion, serum cTn-I levels were found to increase to some extent in one third of stable angina patients who have an acute ischemic episode induced by treadmill exercise test.