1 Results Polymer electrolytes are used as ion conductors in batteries and fuel cells.Simple systems consist of a polymer matrix complexing an inorganic salt and are fully amorphous at the temperatures of interest.Both cations and anions are mobile and contribute to charge transport.Most studies on polymer electrolytes use the electrical conductivity to characterize the ion mobility.However,conductivity measurements cannot discriminate between cations and anions.This paper reports some recent results from radiotracer diffusion experiments performed on electrolytes consisting of poly(ethylene oxide) (PEO) and sodium iodide (NaI)[1-3].It is found that the self-diffusivities of cations and anions show differences in magnitude and temperature dependence[1].In addition,the measured dc conductivities are smaller than corresponding data calculated from the tracer diffusion coefficients.The discrepancy can be explained within a model[2] that makes allowance for the formation of mobile cation-anion pairs. 1 Results Polymer electrolytes are used as ion conductors in batteries and fuel cells. Simple systems consist of a polymer matrix complexing an inorganic salt and are fully amorphous at the temperatures of interest. These cothions and anions are mobile and contribute to charge transport. Most studies on polymer electrolytes use the electrical conductivity to characterize the ion mobility. However, conductivity measurements can not discriminate between cations and anions. This paper reports some recent results from radiotracer diffusion experiments performed on electrolytes consisting of poly (ethylene oxide) (PEO) and sodium iodide (NaI) [1-3] .It is found that the self-diffusivities of cations and anions show differences in magnitude and temperature dependence [1]. Addition, the measured dc conductivities are smaller than corresponding data calculated from the tracer diffusion coefficients The discrepancy can be explained within a model [2] that makes allowance for the formation of mobile cation- anion pairs.