To assess the reproducibility of ergometric parameters at the ischemic threshold, 160 patients, with coronary artery disease and exercise-induced S-T segment depression (102 with previous AMI), were evaluated by means of two control exercise tests performed, in pharmacological wash-out, on different days within 48 hours. The mean values of work load (WL), heart rate (HR) and double product (DP) did not show any statistical difference between the two exercise tests at 0.1 mV S-T depression (ischemic threshold), recorded by a computer assisted electrocardiograph system (Marquette CASE); on the contrary blood pressure (BP) slightly, but significantly (p less than 0.05) decreased at the second test (173.9 +/- 27.2 vs 179.8 +/- 25.8). The variability of the DP values in each subject at 0.1 mV S-T depression, expressed as numerical (delta) and percentage (delta %) differences, exhibited normal distributions. The delta DP showed a mean +/- 1 SD of -157.5 +/- 3271.5 beats x mmHg/min and the delta % DP a mean of +/- 1 SD of 1.46 +/- 16.4%. The values within a standard deviation from the mean (from +3114 to -3429 when numerical differences and from +17.8 to -14.9 when percentage differences) were used for defining the reproducibility of the ischemic threshold. No correlation was found between the delta % DP and the percentage differences in work load at the ischemic threshold. So, DP being more strictly related to MVO2, appears more apt in defining the ischemic threshold reproducibility. A good correlation (r = 0.821) was found between delta DP and delta % DP.(ABSTRACT TRUNCATED AT 250 WORDS)