  A kinetic theory for relativistic gases in the presence of gravitational
fields is developed in the second post-Newtonian approximation. The
corresponding Boltzmann equation is determined from the evolution of the
one-particle distribution function with respect to the proper time along the
world line of the particle. From the knowledge of the equilibrium
Maxwell-J\"uttner distribution function in the second post-Newtonian
approximation the components of the particle four-flow and energy-momentum
tensor are obtained. The Eulerian hydrodynamic equations for the mass density,
mass-energy density and momentum density in the second post-Newtonian
approximation are determined from the Boltzmann equation. It is shown that the
combination of the hydrodynamic equations of mass and mass-energy densities
leads to the hydrodynamic equation for the internal energy density in the first
post-Newtonian approximation.
