Abstract: A non-destructive method for using the mechanical Barkhausen noise phenomenon, caused in fereromagnetic materials by the dislocation motion and the changing external mechanical loading, especially in determining the fatigue strength of the material. The test piece is cyclically loaded with continuously or incrementally increasing amplitude in the presence or absence of a stable magnetic field by which the test piece is magnetized and, simultaneously, measurement is made of the maximum value obtained as a function of one of: the effective value, the size distribution and the mean value of the mechanical Barkhausen noise pulses induced during fatigue of the test piece. The loading amplitude at which such maximum value is reached corresponds to a fatigue strength equal to the fatigue limit of the test piece, the latter having been subjected to a prior loading process to create a lattice defect pattern in the test piece when no stable magnetizing field is present.