This investigation concerns an analysis of the effect, on the rate of resonance energy transfer between a pair of chromophores (the donor and acceptor), of a third chromophore species in their vicinity. Particularly when it is polar, the third body can exert an electrostatic influence on the energy-exchanging species that may result in a significant increase or decrease of their transfer rate. Furthermore it is shown how the presence of the third species can effectively "switch on" the energy transfer process, under circumstances where conventional energy transfer is forbidden due to orientational effects or on symmetry grounds. For example it is indicated that it is possible to instigate energy transfer when the salient acceptor or donor transitions are one-photon forbidden. In addition to results for structurally rigid systems, a rotationally averaged result applicable to fluids or disordered systems is presented.(C) 2002 American Institute of Physics.