The purpose of this study is to determine the in-vivo ultrafiltration coefficient for different sizes of xevonta High-Flux dialyzers following FDA guidelines.

Inclusion Criteria:

• Written informed consent obtained from patient or parents/ guardian.
• Subject age >= 18
• Effective blood flow 350 ml/min and dialysate flow of 500 ml/min
• On hemodialysis for a minimum of 3 months
• Use of Cimino- or Gore-tex shunts
• Routine dialysis-treatment for 240 min
• Documented dialysis adequacy parameter that has been stable for past 3 months
• Plan to dialyze at participating hemodialysis centre for at least 3-months duration.
• Free from any currently known unusual clotting or access problems
• Hepatitis B surface antigen (HbsAg) negative, documented within the past 90 days or Hepatitis B surface antibody (anti-HBs) positive.
• Anti Hepatitis C Virus (Anti-HCV) negative, documented within the past 90 days
• Anti Human Immunodeficiency Virus (Anti HIV) negative, documented within the past 90 days
• Hematocrit (HCT) between 25 and 40% or haemoglobin (Hb) not less than 8 g/dL, as documented 14 days prior to the first treatment

Exclusion Criteria:

• Patients who are unable to tolerate an effective blood flow of 350 ml/min
• Patients using catheter for dialysis
• Pregnant or nursing woman. Women of childbearing potential must agree to avoid pregnancy during the study period by use of hormonal contraception (implantable; patch; oral) and/ or double-barrier methods (any double combination of: IUD; condom with spermicidal gel; diaphragm; sponge; cervical cap)
• Previous plan for extended absences from the participating hemodialysis centre
• Expected to be transplanted (living related donor) within the maximum of 3 months for the study period
• Any serious medical conditions or disability, which in the opinion of the investigator, would interfere with treatment or assessment or preclude completion of the study