To clarify the effects of correction of anemia with recombinant human erythropoietin (rHuEPO) on blood coagulation, fibrinolysis and endothelium, these markers were examined in 19 regular hemodialysis patients before and 4, 8, 12 weeks on rHuEPO treatment, and 5 weeks after the end of treatment. Hematocrit significantly increased from 22.8 +/- 2.0 to 31.1 +/- 2.7% at 12 week (p < 0.001). Coagulation and fibrinolysis markers did not show significant changes except for minor and transient alteration of protein C, thrombin-antithrombin III complex and alpha 2-plasmin inhibitor plasmin complex (PIC) throughout the treatment. Endothelin and 6-keto-prostaglandin F1 alpha (PGF1 alpha) significantly increased from 6.1 +/- 4.5 to 14.2 +/- 2.9 pg/ml (p < 0.001) and from 51.9 +/- 14.7 to 66.5 +/- 18.5 pg/ml (p < 0.05) at 12 week, respectively. Human atrial natriuretic peptide (ANP) significantly decreased from 277.9 +/- 88.6 to 179.4 +/- 73.3 pg/ml at 12 week (p < 0.001). Endothelin and PGF1 alpha after 6 month treatment with rHuEPO showed high values as same as those of 12 weeks. These data suggests that rHuEPO therapy did not affect blood coagulation and fibrinolysis, however exerts effects on the endothelium. Changes in endothelial function after rHuEPO may be one of the pathogenetic mechanisms of hypertension and may contribute to a decrease in thrombotic complications.