Background and aims: Assessment of vascular function is important in linkingpathophysiology with clinical disease. Endothelial dysfunction is recognized to bean early feature of arterial diseases in CKD patients. In the current study we triedto assess the endothelial dysfunction (using vWF) in ESRD patients and to clarifythe role of dialysis in the progression of endothelial injury. In addition, we tried toevaluate the possible role of erythropoietin therapy on progression of endothelialinjury. To achieve this, the study was designed on 2 modules, humans and animals. Methods and results:The human study:Thirty subjects were included in thisstudy and classified into three groups:Group (I): control group (n=10).Group (II):ESRD patients pre-dialysis group (n=10).Group (III): ESRD patients dialysisgroup (n=10). Blood pressure,Blood hemoglobin, Serum urea, creatinine,cholesterol, triglycerides & Plasma vWF were measured.The animal study:Thirtymale albino rats were included in this study and divided into three groups, 10 ratseach:Group (I): control group Group (II): Experimentally induced renal failuregroup Group (III): Experimentally induced renal failure group with EPO hormonetherapy. Renal function was assessed by measuring serum urea andcreatinine.Endothelial dysfunction was evaluated by measuring plasma vWF.Ourresults showed significantly increased plasma vWF in all ESRD patients (both thepre-dialysis and the dialysis groups) denoting the presence of endothelialdysfunction in these patients. The increase in vWF concentrations directlycorrelated with those of urea, creatinine, Hb and triglycerides, but did not correlatewith cholesterol.However, when the pre-dialysis and the dialysis groups werecompared together, there was a significant decrease in plasma vWF in the dialysisgroup. This provided an evidence for improvement of endothelial dysfunction byhemodialysis.In addition, this study revealed that treatment of uremic anemia byerythropoietin hormone studied in experimental animals) was accompanied bysignificant reduction in plasma vWF. The reduction in vWF concentration waspositively correlated with those of urea and creatinine. This suggests a beneficialrole for erythropoietin therapy on progression of endothelial injury.