Patients will be treated with hemodiafiltration (HDF) in postdilution mode, as a control therapy, during 9 weeks. During week 5 the 1st intervention treatment, predilution hemofiltration (HF) or predilution HDF, will be performed as a midweek session. After 4 additional weeks of control therapy the other intervention treatment will be performed. Samples will be taken during week 4, 5 and 9: from inlet blood flow (0, 30, 60, 120 and 240 min), from outlet blood flow and dialysate outflow (30, 60, 120 and 240 min).

Inclusion Criteria:

• stable on hemodialysis >= 6 months
• of which presently on high-flux HD >= 1 month
• 18 years < age < 85 years
• blood flow rate >= 300ml/min

Exclusion Criteria:

• expected survival < 1 year
• expected transplant within < 1 year
• infectious diseases
• pregnancy
• chronic inflammation condition
• treated with single needle dialysis
• presently treated with hemodiafiltration or low-flux hemodiafiltration
• expected intradialytic body weight gain >= 4kg