Control methods of a dialysis machine for allowing the dialysate-side detection of a recirculation in an arteriovenous shunt of a patient during ongoing hemodialysis are described. A sensor is arranged downstream of a dialyzer and detects a change of a physicochemical parameter PD of outflowing dialysis fluid. Control elements are provided to guide the dialysis fluid in a selected manner through the dialyzer or pass it by. Recirculation may be determined by passing the dialysis fluid by the dialyzer so that the dialysis fluid is guided unchanged along the sensor for calibration, switching the control elements after optional sensor calibration such that the dialysis fluid flows through the dialyzer, and adjusting a desired first blood flow value BF1 in the blood-side extracorporeal circulatory branch so that between an inlet of the extracorporeal circulatory branch and an outlet a recirculation R and, a first clearance K1 are adjusted and the parameter detected by the sensor adopts a corresponding value PD1, changing the first blood flow value BF1 to a second blood flow value BF2, wherein a second clearance K2 is adjusted, and accordingly at the sensor a new parameter value PD2 is provided and detected, and determining the recirculation R by the course of change from the parameter value PD1 to the parameter value PD2.
