  It is pointed out that string-loop effects may generate matter couplings for
the dilaton allowing this scalar partner of the tensorial graviton to stay
massless while contributing to macroscopic gravity in a way naturally
compatible with existing experimental data. Under a certain assumption of
universality of the dilaton coupling functions (possibly realized through a
discrete symmetry such as S-duality), the cosmological evolution drives the
dilaton towards values where it decouples from matter. At the present
cosmological epoch, the coupling to matter of the dilaton should be very small,
but non zero. This provides a new motivation for improving the experimental
tests of Einstein's Equivalence Principle.
