A control device for controlling or regulating a blood treatment apparatus for treating blood by means of a single-needle method, wherein the blood treatment apparatus to be controlled or regulated comprises: - a blood pump , connectable to a blood hose set for conveying blood through the blood hose set , wherein the blood pump is operable in a withdrawal direction; - a return pump, arranged to convey fluid towards the blood hose set or a portion thereof and/or towards the patient in a return direction during use of the blood treatment device ; wherein the control device is configured, to perform a method by means of the blood treatment apparatus , the method encompassing the following steps: a) operating the blood pump in a withdrawal direction, in which blood is withdrawn from the patient blood circuit and pumped along a patient hose line into the blood hose set , into which a blood filter with a blood chamber and a dialysis liquid chamber is integrated, the blood chamber and the dialysis liquid chamber being separated from one another by a semi-permeable membrane ; and b) operating the return pump such that blood is pumped out of the blood hose set and pumped along the patient hose line back into the patient blood circuit; wherein steps a) and b) are carried out alternately several times; wherein the method further comprises the following step: - controlling and/or monitoring the method by or under analysis of the pressure measurement values and/or the motor electricity consumption of at least one pump; characterized in that , that blood is not stored in a blood-side single-needle chamber between its withdrawal in step a) and its return in step b). - a blood pump , connectable to a blood hose set for conveying blood through the blood hose set , wherein the blood pump is operable in a withdrawal direction; - a return pump, arranged to convey fluid towards the blood hose set or a portion thereof and/or towards the patient in a return direction during use of the blood treatment device ; wherein the control device is configured, to perform a method by means of the blood treatment apparatus , the method encompassing the following steps: a) operating the blood pump in a withdrawal direction, in which blood is withdrawn from the patient blood circuit and pumped along a patient hose line into the blood hose set , into which a blood filter with a blood chamber and a dialysis liquid chamber is integrated, the blood chamber and the dialysis liquid chamber being separated from one another by a semi-permeable membrane ; and b) operating the return pump such that blood is pumped out of the blood hose set and pumped along the patient hose line back into the patient blood circuit; a) operating the blood pump in a withdrawal direction, in which blood is withdrawn from the patient blood circuit and pumped along a patient hose line into the blood hose set , into which a blood filter with a blood chamber and a dialysis liquid chamber is integrated, the blood chamber and the dialysis liquid chamber being separated from one another by a semi-permeable membrane ; and b) operating the return pump such that blood is pumped out of the blood hose set and pumped along the patient hose line back into the patient blood circuit; wherein steps a) and b) are carried out alternately several times; wherein the method further comprises the following step: - controlling and/or monitoring the method by or under analysis of the pressure measurement values and/or the motor electricity consumption of at least one pump; - controlling and/or monitoring the method by or under analysis of the pressure measurement values and/or the motor electricity consumption of at least one pump; characterized in that , that blood is not stored in a blood-side single-needle chamber between its withdrawal in step a) and its return in step b). <EOS>