  Within the finite-temperature Greens-function formalism we study the equation
of state of a hot interacting pion gas at zero chemical potential. Employing
realistic $\pi\pi$ meson-exchange interactions we selfconsistently calculate
the in-medium single-pion selfenergy and the $\pi\pi$ scattering amplitude in
the quasiparticle approximation. These quantities are then used to evaluate the
thermodynamic potential, $\Omega_\pi$(T), from which the state variables:
pressure-, entropy- and energy-density can be derived. In contrast to earlier
calculations based on the low-energy Weinberg Lagrangian we find an overall
increase as compared to the free-gas results. We also consider the possibility
of a dropping $\rho$-meson mass as suggested by the 'Brown-Rho Scaling' law.
