Cast films were prepared from polybenzimidazole and a polyimide as well as from their blends over the whole composition range. The solvent was N,N’-dimethyl acetamide (DMAc), which was removed by washing with water and drying. The amount of solvent retained by the films depended on sample preparation conditions and significantly influenced the stability of the polymer. Vapour absorption and FTIR studies have shown that solvents enter into strong interaction with the polymers, especially with the polybenzimidazole component. The thorough removal of solvents is an essential condition for the utilization of films prepared from these polymers.