An apparatus for measuring recirculation using thermodilution during extracorporeal blood treatment including a temperature varying unit arranged to cyclically heat and/or cool blood in a venous tube segment of the blood tube system for a quasi-continuous recirculation measurement； and a detecting device configured to measure a variation of a physical parameter resulting from the heating and/or cooling. The detecting device is arranged to detect, in a case free from recirculation, a first physical parameter and to detect, in a case afflicted with recirculation, a physical parameter varied by the cooling and/or heating of the blood by the temperature varying unit as a second physical parameter in the blood tube system. A method for measuring recirculation carries out appropriate steps.
