Estrogen therapy has been associated with reduced risk of coronary heart disease events in observational studies of postmenopausal women. Although favorable effects of estrogen on lipoprotein cholesterol levels probably account for much of this benefit, direct vascular effects (vasomotor, hemostatic, anti-inflammatory) regulated by nitric oxide (NO) may also be of importance. We have recently shown that vasodilator effects of estrogen in the coronary circulation are due to enhanced bioactivity of NO released from the endothelium. Estrogen has been shown to stimulate synthesis and activity of the enzyme NO synthase with enhanced NO synthesis in endothelial cells in culture. Because L-arginine is the natural substrate for the enzyme NO synthase, we propose that the combination of L-arginine and estrogen might have additive vasomotor, hemostatic and anti-inflammatory effects in hypercholesterolemic postmenopausal women.