The effects of recombinant human erythropoietin (rHuEPO) on endothelial vasoactive substances were evaluated in 19 regular hemodialysis patients. Blood cell counts, plasma endothelin (ET), alpha-human atrial natriuretic peptide (ANP), platelet activating factor (PAF), 6-keto-prostaglandin F1 alpha (PGF1 alpha), and 11-dehydro-thromboxane B2 (TXB2) were evaluated before rHuEPO treatment; at 4, 8, and 12 weeks during treatment; and 5 weeks after the end of treatment. PAF and TXB2 remained unchanged during the study period, PGF1 alpha and ET significantly increased, and ANP decreased along with an improvement in the anemia. Since endothelial vasoactive substances changed significantly during rHuEPO therapy, the correction of anemia with rHuEPO may affect endothelium.