  We derive a linearized kinetic equation for fermionic excitations with an
ultrasoft momentum, g^2T, from the Kadanoff-Baym equation in a Yukawa model and
quantum electrodynamics (QED) at extremely high T, where g is the coupling
constant. We show that this equation is equivalent to the self-consistent
equation in the resummed perturbation theory used in the analysis of the
fermion spectrum with the ultrasoft momentum. Furthermore, we derive the
equation that determines the n-point function with external lines for a pair of
fermions and (n-2) bosons with ultrasoft momenta in QED.
