  The kinetic theory of dilute gases to first order in the gradients yields
linear relations between forces and fluxes. The heat flux for the relativistic
gas has been shown to be related not only to the temperature gradient but also
to the density gradient in the representation where number density, temperature
and hydrodynamic velocity are the independent state variables. In this work we
show the calculation of the corresponding transport coefficients from the full
Boltzmann equation and compare the magnitude of the relativistic correction.
