  We investigate the Casimir-Polder interaction between two atoms one of which
is excited. We show that the perturbation theory results in divergence of
integrals for the interaction between an excited atom and a media of dilute
gas. We considered the interaction between two atoms embedded in a dielectric
medium. The non-perturbative method used in this paper shows that the
interaction between the atoms is suppressed due to absorption of photons by the
medium. Now the integrals are divergent no more. Interaction between two media
of dilute gases is considered for the case of high temperatures.
