Device for the recognition of complications during an extracorporeal blood treatment with a blood treatment device, in which the blood to be treated flows in an extracorporeal blood circuit through the blood chamber of a dialyzer divided by a semipermeable membrane in the Blood chamber and a chamber for dialysate fluid and dialysate fluid flows in a dialysate fluid circuit through the dialysate chamber for dialysate fluid, presenting the monitoring equipment: means (18) for changing a physical or chemical characteristic variable of blood in the extracorporeal blood circuit (6), means (18) for changing a physical or chemical characteristic variable of the dialysate liquid in the dialysate liquid circuit (7), means (13, 17； 25, 26) for measuring variables physical or chemical characteristics of blood or dedialized liquid, a first equipment (27) for monitoring of the recirculation of the blood treatment that interacts in such a way with the means to change a physical or chemical characteristic variable of the blood and the means to measure a physical or chemical characteristic variable of the blood or dialysate fluid, which recirculation can be monitored at basis of a change of the physical or chemical characteristic variable of the blood, a device (29) for monitoring the dialysis or blood treatment clearance that interacts in such a way with the means to change a physical or chemical characteristic variable of the blood dialysate liquid and the means for measuring a physical or chemical characteristic variable of the blood or dialysate liquid, which can monitor the dialysis or clearance based on a change of the measured chemical or physical characteristic variable of the dialysate liquid, characterized in that the equipment (29) for monitoring the dialysis or clearance Rationing is configured as a second device for the supervision of recirculation, and recirculation can be monitored based on the verification of the change in dialysis or clearance and an evaluation tea
