The invention relates to a dialysis device (1) comprising a dialysate circuit, which contains a first dialyzer (3) and a second dialyzer (5), wherein the first dialyzer (3) can be connected to a blood circuit of a patient by means of a blood feed (11) and a return (13), a drain for a retentate flow (Q) from the dialysate circuit is provided at the second dialyzer (5), and a diffusate flow (Q) of the second dialyzer (5) in the dialysate circuit is conducted to the first dialyzer (3). The second dialyzer (5) comprises a filter membrane having a cut-off value of at least 500 Da, and the first dialyzer (3) comprises a filter membrane having a higher cut-off value than the second dialyzer (5).
