It was established using the EPR method that a magnetic field ( B =0.6 T) does not affect the process of the appearance of free radicals that are formed as a result of the breaking of covalent chemical bonds in macromolecules of mechanically loaded fibers of polycaproamide. On this basis, as well as on the basis of some other data, doubts were cast on the possibility of using the assumption (frequently discussed in the literature) on the influence of a magnetic field on the rate of transformation of defect complexes due to singlet-triplet transitions upon the fluctuational lengthening of covalent bonds in such complexes for explaining some manifestations of the magnetoplastic effect in ionic crystals.