  In Scalar-Tensor theories of gravity, the expansion rate of the universe in
the past may differ considerably from the standard one. After imposing the
constraints coming from nucleosynthesis, CMB, type Ia supernovae, and solar
system tests of General Relativity, we consider the expansion rate of the
universe at WIMP decoupling, showing that it can lead to an enhancement of the
dark matter relic density of some orders of magnitude with respect to the
standard case. This effect may have a deep impact on most popular candidates
for dark matter, as the supersymmetric neutralino.
