Coronary arteriographic findings in patients with acute transmural inferior infarction were studied from 57 patients (51 men and 6 women). Their ages ranged from 28 to 72 years with a mean of 50 years. Twenty-six patients (Group A) had minimal (less than 0.1 mV) or no precordial ST-segment depression. Thirty-one patients (Group B) had precordial ST-segment depression of 0.1 mV or more. The two groups showed consistent differences in frequency of the left anterior descending artery (LAD) stenosis, multivessel disease, mean peak plasma creatinine phosphokinase (CPK, IU/L), and mean ejection fraction. For Group A vs B, these differences were: LAD stenosis, 31% vs 68%, multivessel disease, 35% vs 81%, mean peak plasma CPK, 1283 versus 1904, and mean ejection fraction, 60.5% vs 45.3%. The incidence of abnormal anterolateral and posterobasal wall motion in Group B was more (p less than 0.01 and p less than 0.05 respectively) than in Group A. All patients in Group B who had precordial ST-segment depression of 0.3 mV or greater, had LAD stenosis. There was no relation between the duration of ST-segment depression and the presence of LAD stenosis. Also, there was no correlation between the presence of collateral circulation and the development of ST-segment depression. The Group B patients tended to have more complications in the acute phase and in the follow up period (p less than 0.05) than did those in Group A. It is concluded that precordial ST-segment depression in acute inferior wall infarction is probably related to anterior injury due to LAD stenosis and these patients were shown to have more severe coronary artery disease, more depression of their ejection fractions, and more myocardial damage than patients without this finding. The earliest recorded ECG is most valuable in identifying the high risk patients. The presence of LAD stenosis in patients with inferior wall infarction who have precordial ST-segment depression of 0.3 mV or more are likely.