Male first degree relatives of acute myocardial infarction patients differ from a control population by virtue of their low HDL cholesterol. The results are compared with those obtained previously in women and children who are first degree relatives of coronary patients. Low HDL cholesterol (Fig. 5) is a familial feature of first degree relatives of acute myocardial infarction patients. This observation is of considerable interest in view of the role of HDL cholesterol in the development of atherosclerosis.