Solutions to problems of pure elastoplastic torsion in surface-plasticized and surface-hardened rods are given. The distribution of residual tangential stresses along the rod radius is shown to have an oscillating and sign-alternating character in both cases. In surface-plasticized rods, in contrast to surface-hardened rods, the residual stresses in the external layer always have the opposite sign with respect to the active loading stresses produced by the outer torsional moment. Conclusions have been drawn about the character of the defect structure changes as well as about the conditions of sample fracture under cyclic torsional tests during the action of alternating outer force moments.