The potentiometric behavior of DEAE-dextran base in aqueous solutions of varying ionic strengths was investigated. Owing to the presence of three different basic groups in the compound, the analysis of the titration curves obtained is quite complicated. Therefore, only the titration range of one of the basic groups present was analyzed in detail and the values of the electrostatic potential at the surface of the polyion were obtained. These values were compared with those calculated from a cylindrical model for the polyion assuming a uniform distribution of charges on the surface. Agreement between the two sets of values is rather poor, which indicates that the model is inappropriate.