Polymer electrolytes consisting of ethyl magnesium bromide solved in poly(ethylene oxide) have been prepared, containing about one molecule of tetrahydrofuran or dibutylether per magnesium ion. Using these gel-like electrolytes, magnesium ion reduction and reoxidation is demonstrated, and the dependence of conductivity on temperature and composition of the electrolyte system is studied. Best results were obtained with a magnesium content of 5-6 wt.% magnesium, corresponding to an ethylene oxide unit to magnesium ratio of 4:1. At 50 degrees C, these electrolyte systems show conductivities in the range of 10(-5)-10(-4) S cm(-1). Enhanced conductivity is found for systems with a higher content of monomer ether per magnesium.