Studies have been made of the effect of neutron irradiation on the resistivity and magnetoresistivity of the alloy AuCu when subjected to various pre‐irradiation thermal and mechanical treatments. The specimens were exposed to estimated fast neutron fluxes up to 7.3×1018neutrons/cm2in the Brookhaven pile. In the case of thermally disordered specimens, the effect of the irradiation was to decrease the resistivity in completely disordered states and to increase the resistivity in completely ordered states;viz., there was some tendency for specimens to reach intermediate degrees of order. The effect on mechanically disordered specimens was to increase the resistivity in all cases. The irradiation effected a larger percentage change in in the coefficient of magnetoresistivity than in the resistivity.