  A systematic study of low mass dilepton production from $\pi-\rho$
interactions in a hot medium is presented. Applying finite temperature
perturbation theory the dilepton rate, respectively the virtual photon rate, is
computed up to order $g_\rho^2$. For dilepton masses below the $\rho$ the
two-body reactions $\pi\pi\to \rho \gamma^*$, $\pi\rho\to \pi \gamma^*$, and
the decay process $\rho \to \pi \pi \gamma^*$ give significant contributions.
Non-equilibrium contributions to the thermal rate are estimated, including the
modification of the particle distribution function with non-zero pion chemical
potential. The comparison of the dilepton rate with the recent data measured in
nucleus-nucleus collisions at SPS energy by the CERES Collaboration is also
performed. It is shown that the additional thermal dileptons from $\pi-\rho$
interactions can partially account for the access of the soft dilepton yield
seen experimentally.
