The cross section for polarized and unpolarized electron-proton scattering is calculated taking into account radiative corrections in leading and next-to-leading logarithmic approximation. The expression of the cross section is formally similar to the cross section of the Drell-Yan process, where the structure functions of the electron play the role of Drell-Yan probability distributions.

The interference of the Born amplitude with the two photon exchange amplitude (box-type diagrams) is expressed as a contribution to K-factor. It is calculated under the assumption that proton form factors decrease rapidly with the momentum transfer squared and that the momentum is equally shared between the two photons. The calculation of the box amplitude is done when the intermediate state is the proton or the Delta-resonance.

The results of numerical estimations show that the present calculation of radiative corrections can bring into agreement the conflicting experimental results on proton electromagnetic form factors and that the two photon contribution is very small.