The electrochemical impedance of Na+ ion conducting zeolite Na-ZSM-5 contacted with gold electrodes is measured. Complementary impedance measurements of the same material contacted with Na+ ion conducting Na2CO3 enabled the separation of volume and electrode parts of the impedance. Both volume and electrode impedances consisted of multiple components. Possible underlying mechanisms are discussed in view of the application of zeolites as sensitive materials in solid-state ionic gas sensors. (c) 2006 Elsevier B.V. All rights reserved.