  We describe the impact of the full one-loop EW terms of O(alpha_s alpha_EM^3)
entering the electron-positron into three-jet cross-section from \sqrt{s}=M_Z
to TeV scale energies. We include both factorisable and non-factorisable
virtual corrections, photon bremsstrahlung but not the real emission of W and Z
bosons. Their importance for the measurement of alpha_S from jet rates and
shape variables is explained qualitatively and illustrated quantitatively.
