Acoustoelasticity is a technique of nondestructive evaluation which relates changes in the stress state acting on a body to changes in the speeds at which waves propagate through the body. The nature of the acoustoelastic effect is well understood under elastic deformations and has been studied under plastic deformations of a polycrystalline aggregate [1–4]. While several phenomenological theories [5–7] have been proposed to describe the effect of plasticity on the acoustoelastic response, the roles of the various microstructural mechanisms which contribute to this effect have not been clearly identified. The purpose of the present work is to examine the effects of two specific mechanisms: the reorientation of grains which accompanies plastic deformation and the motion of dislocations under the applied forces.