  The steps essentially involved in the evaluation of transport coefficients in
linear response theory using Kubo formulas are to relate the defining {\em
retarded} correlation function to the corresponding {\em time-ordered} one and
to evaluate the latter in the conventional perturbation expansion. Here we
evaluate the viscosities of a pion gas carrying out both the steps in the {\em
real time} formulation. We also obtain the viscous coefficients by solving the
relativistic transport equation in the Chapman-Enskog approximation to leading
order. An in-medium $\pi\pi$ cross-section in used in which spectral
modifications are introduced in the propagator of the exchanged $\rho$.
