Different ECG criteria are evaluated with respect to their ability to identify individuals with critical lesions of the coronary arteries in a population of patients with severe angina. Six chest leads and the limb leads were recorded in 85 patients by computer during maximal, symptom-limited exercise ECG testing. Averaging of ECG complexes enhances the signal quality and makes it possible to use measurements of the limb leads recorded during exercise. 14 patients with abnormal Q waves in lead V2 were excluded from ST analysis. In the remaining 71 patients, more than 1/3 mm ST depression in lead I and/or more than 2.0 mm ST depression in any of the chest leads had a sensitivity of 85% and a specificity of 67% for lesions in the main stem and/or proximal LAD and/or three-vessel disease. The predictive value of a positive test was 83 %. This and other criteria were evaluated for different disease groups and at different stages during the exercise test.