It was hoped that the Modifiers Study would answer the major questions raised by the results of the Determinants Study. It tested hypotheses concerning five groups of factors that were potential modifiers of susceptibility to the triggering of acute MI: l) Pharmacologic means of Prevention - that beta blockers, aspirin, angiotensin converting enzyme inhibitors and estrogen use decrease susceptibility to triggers; 2) Timing - that susceptibility does not increase in the morning but does in the winter, and that exogenous rather than endogenous daily rhythms determine onset; 3) Traditional chronic risk factors - that diabetes, hypertension, and smoking increase susceptibility and that regular exercise decreases susceptibility (to triggers other than exertion); 4) Gender - that women are less susceptible to triggering; and 5) Dietary factors - that chronic moderate alcohol use and anti-oxidants decrease susceptibility. To test the hypotheses, 5,700 interviews were needed. By the completion of the Determinants Study in March 1993, over 2,000 interviews were completed. It was estimated that continuation in the Modifiers Study of the 77 interviews per month would provide the required 3,700 additional interviews by December 1997.