  In models with large extra dimensions, where quantum gravity effects become
strong at the TeV scale, the rho-parameter can receive large contributions from
one-loop diagrams involving exchange of multiple graviton and dilaton states.
These contributions are computed, taking into account cancellation of spurious
infrared divergences, and the (finite) results for d = 5 and 6 are compared
with current experimental data. It is shown that 5 large extra dimensions are
incompatible with the data and d = 6 is severely constrained.
