<qa>  What is the main reason for the mortality of end-stage renal disease patients on dialysisRationale: The mortality of end-stage renal disease ESRD patients on dialysis remains high. This may at least be partly due to the insufficient removal of especially protein-bound uremic toxins which have been associated with cardiovascular morbidity and mortality. It is unknown whether the combination of long-hour haemodialysis HD with convection increases the removal of these toxins. Long-hour HD and long-hour haemodiafiltration HDF may also improve haemodynamic stability which is an important factor in treatment quality. The investigators aim to study the removal of uremic toxins in long-hour HD and HDF and to compare the haemodynamics between 4-hour and 8-hour HD and HDF. 