We evaluated the clinical usefulness of the automated ECG analysis system with the Bonner I program based on 1,460 ECGs of which 45.8% were abnormal. Both computer and physician agreed in 93.8% of the 1,460 cases on rhythm analysis, in 89.5% on contour analysis and in 83.6% on both rhythm and contour analysis. Myocardial infarction, LVH and ST abnormality were correctly diagnosed in 81.0, 69.7 and 82.0%, respectively, and error ratios of these diagnoses were 0.50, 0.58, 0.52, respectively. WPW syndrome and electronic pacemaker were rarely diagnosed by the computer. 43 cases diagnosed by the computer as ‘normal sinus rhythm or sinus bradycardia with normal contour ECG’ were of abnormal ECGs. The most frequent causes of disagreement between computer and physician in the diagnosis of myocardial infarction, LVH and ST abnormality were differences in criteria. Since there are several cases of misdiagnoses in the clinically important ECG abnormalities, such as myocardial infarction, it will still be necessary for cardiologists to review all computer-processed ECGs. Nevertheless, the physician’s clerical work would be reduced greatly by using the system when we consider the fact that both computer and physician agreed on the diagnosis of rhythm and contour analysis in 83.6% of the 1,460 cases.