Serum oestradiol and testosterone levels were measured in 50 men who had had a myocardial infarction 4 months previously, in 30 men with acute infarction and in 30 men with essential hypertension without clinical evidence of renal or cardiovascular damage. The results were compared with those of 34 healthy men serving as controls. Patients had higher oestradiol levels than age-matched controls. There was a relationship between oestradiol levels and body weight in the patients. These results indicate that oestradiol may have a role in the process of the vascular damage.