Anhydrous, proton-conducting polymer electrolytes of poly(vinylpyrrolidon) (PVP) with polyphosphoric acid (PPA) were prepared. PVP-x-PPA blends were obtained for 0.5 less than or equal to x less than or equal to 3, where x was the number of moles of PO43- per polymer repeat unit. Fourier transform infrared studies indicated protonation of the carbonyl group in the five-member ring. Thermogravimetric analysis showed that these materials were stable up to about 180 degreesC. Differential scanning calorimetry data demonstrated that the addition of the acid plasticized the material, shifting the glass-transition temperature from 180 degreesC for the pure polymer to -23 degreesC for x = 3. The temperature dependence of the mechanical properties was investigated with shear experiments. The direct-current conductivity increased with x and reached about 10(-5) S/cm at ambient temperature.