Dialysis apparatus including a blood treatment unit having a dialysate chamber and a blood chamber separated by a semipermeable membrane, a dialysate circuit presenting a supply line and a discharge line connected to the blood treatment unit, a preparation device for preparing a dialysate containing a substance present in the blood too and a regulator regulating the concentration of the substance in the dialysate. A blood circuit to circulate extracorporeal blood through the blood chamber a controller that determines a value representative of the concentration of the substance in the blood and are programmed for driving the regulator as a function of the determined value representative of the substance concentration in the blood such that the substance concentration in the dialysate tends towards the substance concentration in the blood.
