Textured Mg alloys exhibit tension – compression strength asymmetry due to mechanical twinning. The distinction arises as the material deforms primarily by slip in one direction and by twinning in the other. In-situ neutron diffraction during cyclic loading in tension and compression of extruded bar allows study of the effect of twinning on subsequent load reversals. The diffraction data reveal the texture evolution and internal stress development as a function of deformation. De-twinning resulted in complete texture reversal during initial cycles, but eventually “fatigued” resulting in some residual twin component.