  I calculate the hydrodynamic limit of the BGK approximation of the Boltzmann
equation for the case of a long stress relaxation time and find that the stress
obeys a viscoelastic constitutive equation. The constitutive equation is
different from standard constitutive equations used for polymeric liquids in
that it is not ``objective'' because inertial effects are important. I
calculate the exact solution for the stresses for simple shear flow and
elongational flow.
