Background/Aim: The mechanisms underlying the aggravation or development of hypertension frequently seen during treatment of renal anemia with epoetins are not fully elucidated. The aim of the present study was to investigate the effects of epoetin alfa on endothelial vasodilatory function in patients with renal anemia and in healthy subjects. Methods: Eighteen preuremic patients with anemia (GFR 23.4 ± 11 SD ml/min, Hb 101 ± 8 g/l) and 10 healthy subjects underwent evaluation of endothelium-dependent vasodilation (EDV) and endothelium-independent vasodilation (EIDV) by means of forearm blood flow (FBF) measurements with venous occlusion plethysmography during local intra-arterial infusions of methacholine (MCh, evaluating EDV) and sodium nitroprusside (SNP, evaluating EIDV). These investigations were performed before and 30 min after an intravenous injection of epoetin alfa (10,000 IU). Ten healthy subjects underwent the same procedure with the exception that saline were given instead of epoetin. The patients were treated with epoetin alfa subcutaneously for 12–19 weeks and revaluated when Hb exceeded 120 g/l. Results: EDV was attenuated after the epoetin injection in both renal patients and healthy subjects. This impairment persisted after anemia had been treated. EDIV and blood pressure remained constant. Saline had no effect on the variables measured. Conclusion: Our results indicate that epoetin alfa impairs endothelial function in renal patients and healthy subjects which may have an impact on vascular complications.