The levels of serum estradiol, testosterone and progesterone were determined in 13 cases of acute myocardial infarction. Thirteen intensive care patients without coronary, hepatic or renal disease, 13 cases of unstable angina and 15 normal subjects. The patients were males ranging from 24 to 56 years of age, the average being 40.4 years. The levels of serum estradiol in the acute myocardial infarction and unstable angina groups were significantly higher than in the normal group, and no difference was found between the normal and intensive care patient. The testosterone levels were significantly lower in the acute myocardial infarction and unstable angina groups than in the normal group. Progesterone levels increased in acute myocardial infarction patients. The estradiol: testosterone ratio was considerably elevated in the acute phase of myocardial infarction, and in unstable angina patients. No difference was found between the intensive care patient and normal groups.