- We consider the feasibility of controlling the energy transfer between an unexcited and an excited atom using microcavities. The excitation-transfer probability is related to the strength of the dipole-dipole interaction and thus the excitation-transfer rates could be increased by enhancing the dipole-dipole interaction. We demonstrate this enhancement with an explicit three-dimensional calculation for a metallic cavity, which we characterize with a realistic dielectric function. We also demonstrate the shifts in cavity resonances from their ideal positions [Formula Presented] ([Formula Presented] is an integer and is the wavelength). 1998 The American Physical Society.