The invention relates to a device for haemodiafiltration comprising an extracorporeal circulation (10) for receiving blood to be cleaned and comprising a haemodialyser and/or haemofilter (20) which is connected to the blood circulation (10), said blood circulation (10) having at least one respective supply line (12, 14) located upstream and downstream of the haemodialyser and/or haemofilter (20), for supplying a substitution fluid. The invention is characterised in that the device also comprises measuring devices for recording the transmembrane pressure and/or haematocrit (HKT) and/or blood density, the measuring devices being connected to a control unit (100) for controlling one or more of the transmembrane pressure, and/or haematocrit (HKT) and/or blood density and said control unit (100) being constructed in such a way that the control is carried out (13, 15) with the aid of at least one of the infusion speeds (Q
