A dialysis machine which includes a preparation system comprising a main line for the dialysis liquid, several supply lines for respective concentrates opening at said main line is disclosed. At a point behind each orifice a respective mixing chamber is arranged and after the latter a respective conductivity probe is disposed. Downstream of the last conductivity probe, a shared pump is arranged. The negative pressure in the main line is adjusted via a pressure control valve which is arranged upstream of the first orifice in the main line. Furthermore, a proportional valve or a digital switching valve is disposed for metering the various concentrates in each supply line. The pressure control valve and the proportional valves or switching valves are controlled in electromagnetic fashion by a central electronic control unit.
