N,N'-Bis-(1H-benzimidazol-2-yl)-isophthalamide (BBImIP) has been synthesized using phosphorus pentoxide-methanesulfonic acid (PPMA) as a solvent and dehydrating agent and investigated as an additive in both sulfonated polysulfone (SPSf) membranes (up to 4.0wt.% BBImIP) and sulfonated poly(ether ether ketone) membranes (up to 3.0wt.% BBImIP). The SPSf/BBImIP blend membranes have been characterized by ion-exchange capacity and proton conductivity measurements as well as single cell and methanol crossover measurements in direct methanol fuel cells (DMFCs). Although the presence of BBImIP in the SPSf/BBImIP blend membranes lowers proton conductivity and cell performance compared to that of plain SPSf, it reduces methanol crossover significantly. On the other hand, the sulfonated poly(ether ether ketone) (SPEEK)/BBImIP blend membranes show cell performance comparable to or better than that of plain SPEEK membrane with reduced methanol crossover. (C) 2008 Elsevier B.V. All rights reserved.