Infrared spectroscopic studies of the effect of the plasticizers ethylene carbonate, tetraethylene glycol, and tetraethylene glycol dimethyl ether on the (PEO)(x)LiCF3SO3 system are reported. These data are augmented by measurements of the ionic conductivity. Relative concentrations of the various ionic species present have been determined as a function of plasticizer content. The plasticizers appear to preferentially interact with the crystalline PEO phase in the (PEO)(x)LiCF3SO3 complexes, although the relative amount of the compound (PEO)(3)LiCF3SO3 decreases with addition of plasticizer. The net Effect of the addition of plasticizer is to create ionically-conducting pathways of amorphous PEO containing dissolved ionic species.