The multiplicity of ${e}^{+}{e}^{\ensuremath{-}}$ or ${\ensuremath{\mu}}^{+}{\ensuremath{\mu}}^{\ensuremath{-}}$ pairs produced at finite temperature is expressed in terms of the photon proper self-energy at finite temperature. The production rate is strongly dependent on the four-momentum ${q}^{\ensuremath{\mu}}$ of the lepton pair and has a resonance at ${q}^{2}=\mathrm{Re}\ensuremath{\Pi}$.