The purpose of this study is to determine whether on-line hemodiafiltration ameliorate the endothelial dysfunction compared with the low flux hemodialysis in end stage renal disease patients on maintenance hemodialysis.

1. On-line hemodiafiltration(OL-HDF) is a technique that combines diffusion with convection in which the large substitution fluid is produced directly from the dialysate. It offers many advantages aside from its safe inflammatory profile, which is attributable to the use of ultrapure dialysate and highly biocompatible dialysis membranes. Due to an improved convective clearance, significantly increased removal of large or protein-bound uremic retention solutes can be achieved, with a potential benefit on cardiovascular morbidity and mortality.
2. Endothelial dysfunction, almost universal in end stage renal disease, is important risk factor for cardiovascular events, and can be evaluated by brachial artery endothelium-dependent vasodilation (flow-mediated dilation) to reactive hyperemia following 5 min of forearm ischemia.
3. The stable HD patients will receive 8-week treatment on OL-HDF or conventional low flux HD and then crossed over to opposite treatment arm. The FMD will be measured by one sonographer, and at the same time whole blood and serum will be sampled and stored for further analysis. The timepoint for measurement is 4-week interval after baseline evaluation.

Inclusion Criteria:

• end stage renal disease on maintenance hemodialysis for more than 3 months

Exclusion Criteria:

• diagnosis of active cardiovascular diseases in 6 months
• elevation of liver enzymes over two fold of upper normal limit in 3 months
• admission for acute infection in 3 months
• untreatable stenosis of vascular access