An alteration in sex hormones has been considered a risk factor for myocardial infarction. In this study, estradiol (E2) and testosterone (T) levels were evaluated in healthy firefighters, patients with myocardial infarction acutely and during their convalescence, patients with no evidence of occlusive coronary artery disease on arteriography, and patients with chronic angina pectoris in whom there was at least one vessel that indicated 50% occlusive coronary artery disease. Although T levels were similar in all groups, E2 levels were substantially higher in patients with myocardial infarction and in patients with chronic angina pectoris. These results support the hypothesis that elevated estrogen levels may be a risk factor for myocardial infarction and coronary artery disease, possibly by promoting clotting or coronary spasm.