  A covariant method is proposed for calculating the amplitudes of processes
involving polarized spin 1/2 particles. It is suitable for calculating the
interference terms in the cross sections of such processes. As an illustration,
expressions are given for the amplitudes of electron-electron scattering in the
lowest order of perturbation theory and expressions for the electron current in
the case of emission of two bremsstrahlung photons in the ultrarelativistic
limit.
