A method for detecting a stenosis located between a blood pump (9) and a treatment device (4) in a blood line (3) of a circuit (2) for extracorporeal blood treatment has been provided. The method includes acquiring first pressure values from a first sensor (13) mounted at a first point of the circuit (2) and second pressure values from a second sensor (14) mounted at a second point, distinct from the first point of the blood line (3) of the circuit (2), and relating at least one first value, related to corresponding pulsating signal amplitudes of the first pressure value, and at least one second value, related to corresponding pulsating signal amplitudes of the second pressure value, with a threshold value, in order to obtain a datum representing a state of the blood line (3), wherein relating comprises performing a ratio between the first value and the second value, and comparing a result of the ratio with a threshold value in order to obtain the datum representing a state of the blood line (3).
