To ascertain the origins and types of irradiation-induced modifications of magnetic properties, toroid and thin-film specimens of permalloys in various states of magnetization were exposed to neutron irradiation. Magnetic hysteresis loop characteristics and magnetic anistropy were measured in the pile, as well as before and after irradiation. The magnetic characteristics of the toroid specimens were severely altered by irradiation, exhibiting increased values of coercive force as well as large changes in hysteresis loop shape. Thin-film specimens of Ni³Fe, on the other hand, had hysteresis loop characteristics which were much less affected by neutron irradiation. However, following irradiation in a magnetic field, applied in the hard direction, the magnetic anisotropy of the thin films was found to decrease significantly. These results are attributed to the development of radiation-enhanced, short-range directional ordering, as well as the interaction of the irradiation-induced defects with the magnetic-domain structure.