It is important for the plant lifetime management to estimate the loss of toughness and other effects, e.g. increase of yield strength and hardness, caused by irradiation. This paper deals with the use of magnetic measurements to determine the irradiation effects on nuclear reactor structural materials. Three types of nuclear reactor materials were studied. Samples of the materials were irradiated with different neutron fluences. The Magnetic Barkhausen Emission was measured using stabilised flux mode, i.e., control of the magnetic flux within the sample to compensate for leakage and variations on the flux. The samples were carefully identified according to position and the cutting direction within the steel forging block. Anisotropy effect due to sample cutting direction was observed and it masks the magnetic signal results induced by the irradiation effects. The results on the specimens cut in the same direction shows correlation with irradiation induced material hardening and its dependence on fluence. Different materials show different hardening levels. Barkhausen emission results were correlated to neutron fluence taking into account the cutting direction.