A device for extracorporeal blood treatment is disclosed that includes a detection equipment for detecting uremic toxins in a used dialysis liquid by measuring the absorbance, the detection equipment being provided at such a position downstream the outflow of the dialysis liquid from a filter element that at least one of the following requirements is fulfilled: a) the filling volume of the fluid line and of the components starting from the outflow of the used dialysis liquid from the filter element to the detection equipment is less than or equal to 100 ml and b) the length of the fluid line starting from the outflow of the used dialysis liquid from the filter element to the detection equipment is at most 250 cm.
