The electrocardiograms and clinical characteristics of 152 patients with chest pain, who had changes only in their ST or T waves, were evaluated. The increase in ST depression was significantly greater (p less than 0.01) in infarction patients than in those without infarction; this was not the case with T wave inversion (p greater than 0.5). Infarction patients with ST depression had a higher incidence of previous myocardial infarction and prior digitalis usage (74% versus 35%, p less than 0.01) and a significantly greater short term (37% versus 12%, p less than 0.05) and long term (52% versus 19%, p less than 0.02) mortality than infarction patients who had T wave inversion alone. This difference was unrelated to infarct size as determined by peak enzyme levels. These two groups, therefore, appear to be clinically distinct, perhaps related to differences in ventricular function and/or extent of coronary artery disease.