  We consider the effects of the time dependence of couplings due to their
dependence on a dilaton field, as occurs in superstring theory, as well as in
gravity theories of the Jordan-Brans-Dicke type. Because the scale parameters
of couplings set by dimensional transmutation depend exponentially on the
dilaton vev, we may obtain stringent limits on the shift of the dilaton from
the requirement that the induced shift in the couplings not vitiate the
successful calculations of element abundances for big-bang nucleosynthesis.
These limits can be substantially stronger than those obtained directly from
the dilaton-induced change in the gravitational coupling.
