Heterogeneous ion-exchange membranes (both cationic and anionic types) have been synthesized by solution casting techniques using polyvinyl chloride (PVC) as binder and ion-exchange resin (-300 + 400 mesh). The binder : resin ratio varied from 60 : 40 to 30:70. The transport behavior of the membranes has been evaluated chronopotentiometrically in sodium chloride (NaCl) solutions of different concentrations. The different parameters E-0 (potential drop across the membrane at the instant of application of current I), E-max (maximum potential drop across the membrane after the application of current I), DeltaE (magnitude of the potential jump across the membrane at transition time tau), Itau(1/2), tau, etc., have been evaluated. The isoconductance points were determined and based on the microheterogeneous model proposed by Zabolotsky and Nikonenko (J. Membrane Sci. 79 (1993) 181) the distribution factors beta has been evaluated for both types of ion exchange membranes. The electroconductivity of the joint gel (kappa) and pure gel phases (kappa') has been determined. At any particular solution concentration the transport number as well as the permselectivity of membranes increases with increased resin content of the membrane. The microheterogeneity factor beta exhibits synchronization among the each set of four different membranes for both the cationic and anionic type. (C) 2003 Elsevier Science (USA). All rights reserved.