Haemodiafiltration (HDF) is renal replacement therapy. It is a method of blood clearance based on the principle of diffuse and convection transport of substances through a semipermeable membrane. The method uses high-flux membranes, usually synthetic ones with a high ultrafiltration coefficient. According to the principle of preparation of a substitution solution HDF is divided into bag methods (substitution solutions in bags), on-line HDF (continual preparation of substitution solution in an apparatus in the course of the procedure) and HDF based on reversed filtration of the dialyzation solution through the membrane of the haemodiafilter. Depending on the length and frequency of the procedure, there is intermittent HDF used in particular in the treatment of chronic renal failure and continual HDF used in acute conditions where renal failure is part of multiorgan dysfunction. Depending on the site of administration of the substitution solution, we differentiate between predilution HDF (the substitution solution is administered into the blood stream before haemodiafiltration) and postdilution HDF (the substitution solution is administered into the bloodstream after the haemodiafilter). HDF methods are highly effective in the elimination of low-molecular and medium-molecular substances. They are effective and well tolerated by patients. They can be used under conditions when standard haemodialysis is associated with circulatory instability or is not sufficiently effective. The author describes principles and possibilities of application of different modifications of HDF methods.