A blood treatment system comprising at least one first device and at least one second device, wherein the first device is a membrane filter for the removal of toxic mediators from blood and the second device is suitable for the removal of granulocytes and monocytes from blood. The first device has a first blood flow path a first blood flow path for conducting blood through and the second device has a second blood flow path. The first and second devices are serially connected in succession in such a way that the first blood flow path is in fluid communication with the second blood flow path.The membrane has an interior filter space in its housing and a semipermeable membrane arranged in the interior filter space, which membrane divides the interior filter space into a retentate chamber and permeate chamber. The housing has a blood inlet device and a blood outlet device that are in fluid communication with the retentate chamber, as well as a permeate outlet for diverting permeate from the permeate chamber. The blood inlet device, the retentate chamber and the blood outlet device form the first blood flow path. The membrane filter has a separation characteristic such that the sieve coefficient for albumin, SKAlb, is within the range from 0.015 to 0.35.
