Sometimes the physicians meet an atypical electrocardiogram in patients with old myocardial infarction and are confused about the decision to have or not the history of myocardial infarction 1). Thus, in order to make up the weak point of electrocardiogram, the biochemical and serological methods are being introduced. Since C-reactive protein test has been introduced as the serological accessory diagnostic method of fresh myocardial infarction, there has been numerous reports made by Kroop and many others. However, in old myocardial infarction, any serological method has not been designed. In this regard the authors examined serologically the sera in patients with myocardial infarction and obtained the results that might be used clinically.