  We discuss the role of gravitational excitons/radions in different
cosmological scenarios. Gravitational excitons are massive moduli fields which
describe conformal excitations of the internal spaces and which, due to their
Planck-scale suppressed coupling to matter fields, are WIMPs. It is
demonstrated that, depending on the concrete scenario, observational
cosmological data set strong restrictions on the allowed masses and initial
oscillation amplitudes of these particles.
