The study investigates the performance of a new dialyzer (Theranova 400) containing a membrane with increased pore sizes. The performance will be determined by the removal of middle molecules (with different molecular size) from the blood compartment. Two different Theranova 400 prototypes (AA and BB) operated in hemodialysis mode will be compared with a Cordiax Fx-80 dialyzer, operated in hemodialysis mode, and with a Cordiax Fx-800, operated in high volume hemodiafiltration mode. Safety events and albumin loss into the dialysate will be monitored

Inclusion Criteria:

1. Patient has end-stage renal disease (Chronic kidney disease stage 5D)
2. Patient is 18 years of age or older
3. Patient is male or female
4. Patient, if female, is non-pregnant; and if capable of becoming pregnant, will be using a medically acceptable means of contraception during participation in the study 5 .Patient has been receiving HD or HDF therapy for >3 months prior to study enrollment and is expected to survive for at least 12 months after enrollment.

6. Patient has a stable functioning native fistula 7. Patient is willing to comply with the study requirements for therapy during the entire study treatment period 8. Patient is capable fo providing written informed consent to participate in the study

Exclusion Criteria:

1. Patient is undergoing single-needle dialysis

2. Patient has an known abnormal k/λ ratio (less than 0.37, or greater than 3.1)

3. Patient has a known active infection and is currently receiving antibiotic treatment

4. Patient has known active cancer

5. Patient has a known positive serology test for human immunodeficiency virus (HIV) or hepatitis B,C or E

6. Patient has a known serious hemostasis disorder

7. Patient has a known monoclonal gammopathy

8. Patient has a known polyclonal gammopathy

9. Patient has a unstable condition as judged by the treating physician based on medical history, physical examination and laboratory testing including (but not limited to) any of the following:

   • Myocardial infarction within the last 3 months
   • Tachyarrhythmia or bradyarrhythmia absoluta
   • Unstable angina pectoris
   • Left ventricular ejection fraction <30%
   • Significant pericardial disease

10. Patient has any other known comorbidity that could, in the opinion of the Investigator, potentially conflict with the study purpose or procedure

11. Patient has a known significant psychiatric disorder or mental disability that could interfere with the patient's ability to provide informed consent and/or comply with protocol procedures

12. Patient has a history of non-compliance with the dialysis prescription, as assessed by the Investigator

13. Patient has participated in another interventional clinical study in the past 3 months, or is currently participating in another interventional clinical study