Device for the treatment of extracorporeal blood, with a dialyzer (1) that is divided into a blood chamber (3) and a dialysis fluid chamber (4) through a semipermeable membrane (2), where the chamber of blood is part of an extracorporeal blood circuit (9) and the dialysis fluid chamber is part of a dialysis fluid system (10)； an apparatus (19) for supplying replacement solution to the extracorporeal blood circuit (9) with a predetermined replacement solution rate and an apparatus (26) for regulating the supply of replacement solution, characterized in that the apparatus (26) for regulating The supply of replacement solution has: means (27) for determining the rheological load of the dialyzer, means (29) for determining the transmembrane pressure or a variable that correlates with the transmembrane pressure, which depends on the pressure of transmembrane, and means for determining the flow resistance of the dialyzer or of a variable that correlates with the flow resistance, which depends on the flow resistance, where the means (27) for determining the rheological load of the dialyzer are designed to so that the rheological load of the dialyzer is determined based on the transmembrane pressure or the variable that correlates with the pressure of transmembrane, which depends on the transmembrane pressure, and based on the flow resistance or the variable that correlates with the flow resistance, which depends on the flow resistance, and means (28) for regulating the rate of replacement solution, which are designed so that the replacement solution rate is regulated based on the rheological load of the dialyzer.Dispositivo para el tratamiento de sangre extracorporal, con un dializador (1) que se encuentra dividido en una cámara de sangre (3) y una cámara de líquido de diálisis (4) a través de una membrana semipermeable (2), donde la cámara de sangre forma parte de un circuito de sangre extracorporal (9) y la cámara de líquido de diálisis forma parte de un sistema de líqui
