The endothelium plays an important role in the regulation of vascular tone and regulation of blood flow. Nitric oxide (NO) is the most important known endothelium-derived vasodilating factor. Prospective studies have shown that hypercholesterolemia impairs endothelial function in different vascular beds. Lowering total cholesterol and particularly LDL-cholesterol with statins leads to an improvement in endothelium-dependent vasodilation in the forearm vasculature. There is strong evidence to suggest that the benefit is not merely related to the decrease in cholesterol-levels. A recent study in the forearm vasculature demonstrated that short-term lipid-lowering therapy improves endothelial function and NO availability already after 3 days of lipid lowering therapy. Whether endothelial function in the renal vasculature of hypercholesterolemic patients is similarly influenced has not yet been addressed adequately. In the present study we investigate whether lipid lowering therapy with rosuvastatin alters renal endothelial function, as assessed by systemic infusion of the NO synthase inhibitor L-NMMA, after 3 and 42 days of therapy.