Rho Parameter Constraints on Models with Large Compact Dimensions

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.