The electrical properties of a membrane containing a single salt M+ X-, with the cation being the only permeable species and the anion the blocked species at the interfaces, are analysed using the network method. The steady-state electrical properties of the system and the small-amplitude ac response of the biased system with a simultaneous dc steady-state electric current have been obtained by simulation with the PSPICE program of a previously obtained network model for a thin-layer electrochemical cell. The results obtained confirm the validity of the network approach to deal with diffusion-migration impedances of electrochemical systems with symmetric, reversible interfacial processes when a dc electric current is superimposed. Some advantages of the present approach over more classical ones are discussed.