The initial ECG in acute myocardial infarction (AMI) was assessed in relation to the mortality during hospitalization and development of acute complications endangering life in 405 cases of AMI (345 patients) admitted during a period of three years. The initial ECG recordings were grouped as "positive" or "negative" according to meticulously defined criteria based on the morphology of the QRS complex, deviations of the ST segment and the polarity of the T waves. The ECG recordings were "positive" in 298 cases (86.4%) and "negative" in 47 cases (13.6%). The mortality during hospitalization in the group with "negative" ECG records was definitely lower than in the group with "positive" ECG records (p less than 0.001, chi 2 = 13.99). On the other hand, no definite differences were observed when the initial ECG was compared with the incidence of arrhythmias endangering life (ventricular fibrillation, ventricular tachycardia, asystoly and 3 degrees atrio-ventricular block) (0.10 less than p less than 0.20; chi 2 = 2.46). The authors thus cannot recommend that the initial ECG is given decisive value as to whether a patient with suspected AMI is to be observed in a coronary unit.