We evaluated 89 patients with predischarge and 6-week post-myocardial infarction treadmill exercise tests to determine the importance of doing repeat tests to identify abnormalities of known prognostic value, and assess the individual variability of treadmill abnormality responses. Nineteen patients (21%) completed only a predischarge exercise test, nine of whom experienced an early cardiac event precluding repeat testing. All nine had a prognostically important treadmill abnormality during the predischarge test. Electrocardiographic ST segment depression was highly reproducible between the early and 6-week tests (k = 0.968). However, angina, inadequate blood pressure response, and ventricular arrhythmias showed limited reproducibility (k = 0.344, 0.50, and 0.166, respectively) and substantial individual variability. Thus, we concluded that: a predischarge treadmill exercise test is important for determining the immediate short-term prognosis of patients after myocardial infarction; and ST segment depression is highly reproducible, whereas other treadmill abnormality responses show substantial variability between the predischarge and 6-week tests.