The relation of resting electrocardiographic (ECG) patterns to angiographic features was assessed in 566 patients with chest pain regarded as definite or probable stable angina pectoris. The indications for catheterization in each patient were determined at the discretion of the attending physician. All patients underwent diagnostic coronary angiography (clinically important coronary artery disease was defined as > or = 70 per cent narrowing of the diameter of at least one major vessel or > or = 50 per cent of the left main coronary artery) and standard 12 lead electrocardiography which was interpreted by 2 cardiologists independently in coordinating centre. The signs of impaired coronary blood flow were assessed by abnormalities of repolarization (among others S-T segment, the T wave), depolarization and presence of disturbances of cardiac rythm. The resting routine electrocardiogram was assigned to one of three categories: normal, nonspecific abnormalities or typical for coronary insufficiency. The typical pattern for ischemia was present in 104 patients (18%), nonspecific abnormalities were present in 185 patients (33%) and electrocardiogram was normal in 277 patients (49%). Sensitivity and specificity of the typical for coronary insufficiency resting ECG was calculated: 23% and 87% respectively for the entire group, 33% and 81% in women, 20% and 93% in men. In the group with normal resting electrocardiographic pattern 55% of patients have significant stenosis in at least one major coronary artery.