Randomized, placebo-controlled, blinded. The minimum diameter of coronary stenotic lesions was measured by angiography before and after three years in a group receiving unopposed estrogen replacement therapy, a group receiving estrogen replacement plus continuous low dose progestin, and a group receiving placebo. The incidence of clinical events was documented in all three groups. Secondary objectives of the trial included examining the effect of chronic and acute estrogen administration on endothelium-dependent coronary vasodilator capacity, plasma lipids and lipoproteins, antioxidant activity, blood pressure, glucose metabolism, and plasma hemostatic factors, as well as on behaviors, physical attributes, and psychosocial parameters. There were four pre-randomization variables in order to pre-stratify. These included current smoking status, insulin dependent diabetes, current lipid-lowering therapy, and the hospital where angiograms were performed.