  This paper summarizes the contribution presented at the {\sl IX Marcel
Grossmann Meeting} (Rome, July 2000). It is stressed, in particular, that a
non-relativistic background of ultra-light dilatons, produced in the context of
string cosmology, could represent today a significant fraction of cold dark
matter. If the dilaton mass lies within the resonant band of present
gravitational antennas, a stochastic dilaton background with a nearly critical
density could be visible, in principle, already at the level of sensitivity of
the detectors in operation and presently under construction.
