The study used an existing resource of frozen blood samples from a cohort of 7,058 postmenopausal women enrolled between 1985 and 1991 for a study of endogenous hormones and cancer. The cohort was followed up to identify incident cases of coronary heart disease. One hundred thirty cases of coronary heart disease (defined as nonfatal myocardial infarction or death from coronary heart disease) were expected to occur by the end of follow-up. A nested case-control study was conducted in which each case was matched to two women from the cohort who were the same age as the case, donated blood around the same time, and were alive and free of heart disease as of the date of diagnosis of the case. Frozen serum samples from cases and their matched controls were analyzed for total estradiol, bioavailable estradiol (the estradiol fraction not bound to sex hormone binding globulin) estrone, total cholesterol, and high- and low-density lipoprotein cholesterol. Conditional logistic regression for matched sets were employed to determine whether estrogen levels were lower in the cases than their matched controls. The association between estrogen levels and cholesterol fractions was also investigated.