The extension of our previous OPE calculations to Q-4 effects, connected with twist-6 operators is discussed. A new type of interaction appears in this order between the struck quark and vacuum fluctuations characterized by the non-zero vacuum average values of (Gμνa)2 and ψψ, the so-called gluon and quark condensates. While the former interaction is absent for Born diagrams, the latter is probably essential, especially for electromagnetic longitudinal structure function. We also discuss the case of the polarized target, in which twist-3 operators enter together with the leading twist-2 ones. We find OPE coefficients for them and determine power Q-2 corrections for polarized scattering.