A study of the polymer electrolyte system containing poly(ethylene oxide), P(EO), with lead perchlorate is presented. The phase diagram, examined over a Pb(ClO4)2 concentration of 0-0.24 mol% by means of differential scanning calorimetry, thermomicroscopy, thermogravimetric analysis, is of the eutectic type. A polymer-salt compound is formed (x similar to 0.09), which melts incongruently at T similar to 420 K. The ionic conductivity in the elastomeric phase reaches 10(-4) Omega(-1) cm(-1). The dielectric relaxation technique is used to investigate the relaxation phenomena at low temperatures, below the glass transition. The results are compared with those previously obtained on P(EO)-based systems containing different perchlorates and other Pb salts.