To determine whether regular administration of lipid modifying drugs (clofibrate, nicotinic acid, estrogen, dextrothyroxine) to men with a documented myocardial infarction would result in significant reduction in total mortality over a five year period. Secondarily, to determine whether the degree to which these drugs changed serum lipids was correlated with any effect on mortality and morbidity rates; to gain further information on the long-term prognosis of myocardial infarction (by studying the control group as intensively as the treatment group); to acquire further experience and knowledge concerning the techniques and methodology of long-term clinical trials; to determine, in a substudy, the effectiveness of aspirin, a platelet inhibitor, in reducing recurrences of myocardial infarction.