  We solve the one-dimensional boost-invariant kinetic equation for a
relativistic massive system with the collision term treated in the relaxation
time approximation. The result is an exact integral equation which can be
solved numerically by the method of iteration to arbitrary precision. We
compare predictions for the shear and bulk viscosities of a massive system with
those obtained from the exact solution. Finally, we compare the time evolution
of the bulk pressure obtained from our exact solution with results obtained
from the dynamical equations of second-order viscous hydrodynamics.
