The electro-osmotic drag coefficient of water in two polymer electrolytes was experimentally determined as a function of water activity and current density for temperatures up to 200 degrees C. The results show that the electro-osmotic drag coefficient varies from 0.2 to 0.6 in Nafion(R)/H3PO4 membrane electrolyte, but is essentially zero in phosphoric acid-doped PBI (polybenzimidazole) membrane electrolyte over the range of water activity considered. The near-zero electro-osmotic drag coefficient found in PBI indicates that this electrolyte should lessen the problems associated with water redistribution in proton exchange membrane fuel cells.