Abstract: A method for extracorporeal treatment of blood includes preparing a treatment liquid from a liquid and two concentrated solutions by circulating the liquid in a preparation conduit at a flowrate Q0; injecting a first concentrated solution containing at least a first ionic substance A and a second ionic substance B into the preparation conduit at a flowrate Q1; and injecting a second concentrated solution containing at least the first ionic substance A into the preparation conduit at a flowrate Q2. The ionic substance B may have a first concentration in the first concentrated solution and a second concentration, different from the first concentration, in the second concentrated solution. The method may also include regulating the injection flowrates Q1 and Q2 in such a way that at any given time the diluted solution resulting from the mixing of the liquid and the concentrated solutions has a desired concentration of the first ionic substance A and a desired concentration of the second ionic substance B.