A device for detecting the recirculation for an extracorporeal blood treatment apparatus, wherein the extracorporeal blood treatment apparatus comprises: an extracorporeal blood circuit with an arterial blood line, which leads to a first chamber of a dialyser or filter divided by a membrane into the first chamber and a second chamber, and a venous blood line, which leads away from the first chamber of the dialyser or filter, a fluid system, which comprises the second chamber of the dialyser or filter, a device for conveying blood at a preset blood flow rate Q b through the arterial blood line into the first chamber of the dialyser or filter and through the venous blood line from the first chamber of the dialyser or filter, a device for supplying substituate to the blood at a preset substituate rate Q s in the arterial blood line upstream of the dialyser or filter, wherein the device for determining the recirculation comprises: a measuring unit for measuring the pressure in the extracorporeal circuit in the arterial and/or venous blood line (6, 7), and an evaluation unit for detecting the recirculation on the basis of the pressure measurement, the device for detecting the recirculation comprising a control unit cooperating with the device for conveying blood and the device for supplying substituate, said control unit being constituted such that, in an operating mode for detecting the recirculation, the device for supplying substituate is controlled in such a way that in a preset time interval substituate is fed at a preset substituate rate Q s to the blood in the arterial blood line upstream of the dialyser or filter, and the evaluation unit being constituted such that the pressure measured by the pressure measuring unit in the arterial and/or venous blood line for the detection of a recirculation is monitored for a change in the pressure characterised in that the device for conveying blood is controlled in such a way that in the preset time interval the preset first blood flow rate Q b1 is reduced to a preset second blood flow rate Q b2. an extracorporeal blood circuit with an arterial blood line, which leads to a first chamber of a dialyser or filter divided by a membrane into the first chamber and a second chamber, and a venous blood line, which leads away from the first chamber of the dialyser or filter, a fluid system, which comprises the second chamber of the dialyser or filter, a device for conveying blood at a preset blood flow rate Q b through the arterial blood line into the first chamber of the dialyser or filter and through the venous blood line from the first chamber of the dialyser or filter, a device for supplying substituate to the blood at a preset substituate rate Q s in the arterial blood line upstream of the dialyser or filter, wherein the device for determining the recirculation comprises: a measuring unit for measuring the pressure in the extracorporeal circuit in the arterial and/or venous blood line (6, 7), and an evaluation unit for detecting the recirculation on the basis of the pressure measurement, the device for detecting the recirculation comprising a control unit cooperating with the device for conveying blood and the device for supplying substituate, said control unit being constituted such that, in an operating mode for detecting the recirculation, the device for supplying substituate is controlled in such a way that in a preset time interval substituate is fed at a preset substituate rate Q s to the blood in the arterial blood line upstream of the dialyser or filter, and the evaluation unit being constituted such that the pressure measured by the pressure measuring unit in the arterial and/or venous blood line for the detection of a recirculation is monitored for a change in the pressure characterised in that the device for conveying blood is controlled in such a way that in the preset time interval the preset first blood flow rate Q b1 is reduced to a preset second blood flow rate Q b2. a measuring unit for measuring the pressure in the extracorporeal circuit in the arterial and/or venous blood line (6, 7), and an evaluation unit for detecting the recirculation on the basis of the pressure measurement, the device for detecting the recirculation comprising a control unit cooperating with the device for conveying blood and the device for supplying substituate, said control unit being constituted such that, in an operating mode for detecting the recirculation, the device for supplying substituate is controlled in such a way that in a preset time interval substituate is fed at a preset substituate rate Q s to the blood in the arterial blood line upstream of the dialyser or filter, and the evaluation unit being constituted such that the pressure measured by the pressure measuring unit in the arterial and/or venous blood line for the detection of a recirculation is monitored for a change in the pressure characterised in that the device for conveying blood is controlled in such a way that in the preset time interval the preset first blood flow rate Q b1 is reduced to a preset second blood flow rate Q b2.