Today, haemodialysis is a recognized standard treatment for patients with chronic kidney disease stage 5. During the haemodialysis treatment session, blood passes from the patient through the extracorporeal circuit and is then returned. The dialyzer represents the greatest surface are of the extracorporeal circuit, as dialysis treatment is essentially based on the removal of small molecular weight solutes down along a concentration gradient, and this depends upon surface area. The ELISIO-H dialyzer differs in design to our current standard dialyzer, the FX100, by having fibers of a greater internal diameter, which potentially allows more internal haemofiltration, leading to an improved clearance of larger molecular weight solutes. It is now thought that these so called "middle molecular weight" solutes are more important in contributing to the clinical condition termed azotaemia, rather than smaller solutes such as urea.