We report an ion-conducting device comprising an ultrathin polyelectrolyte multilayer membrane assembled in a simple manner with water soluble polymers. Under the influence of external solution ionic strength (salt concentration), sites for ion transport are reversibly doped into the membrane. The device exhibits rectifying properties, preferring ions of lower charge, with a saturation ion current limited by diffusion. This system allows for the transduction of chemical potential into ion currents. Current/voltage curves spanning forward and reversed biased regimes are presented, together with linear and hyperlinear salt gating of ion currents. (C) 2004 The Electrochemical Society.