[en] Weak interaction corrections to R = sigma(e⁺e^-→all)/sigma(e⁺e^-→μ⁺μ^-) at high energies are calculated using a quark parton model. It is shown that the correction due to interference between γ and Z mediated annihilations (which would make itself manifest by a variation linear in the square of the centre-of-mass energy) is strongly model dependent. In particular the γ-Z interference contribution to R vanishes identically (to the order gsub(s)sup(4) in the gluon coupling constant) in unified theories of weak, electromagnetic and strong interactions provided the lepton and quark masses are neglected as compared with the energy, and if perturbation theory is valid. (Auth.)