  The coupling between a quantum dynamical system and a two-level system
reservoir is analysed within the framework of the Feynman-Vernon theory. We
stress the differences between this new reservoir and the well-known bath of
oscillators and show that, in order to obtain the Langevin equation for the
system of interest in the high temperature regime, we have to choose a spectral
distribution function $J(\omega)$ which is finite for $\omega=0$.
