In this study, stainless steel electrode alternate current (ac) impedance associated with direct current (dc) polarization measurements were proposed to successfully evaluate the contribution of ionic conductance (t(ion)) to the bulk conductance of polypyrrole (PPy) in various relative humidities (RH). The fraction of t(ion), defined as the ratio of (1/R-i) to ((1/R-i) + (1/R-e)), was used as a quantitative index for the contribution of ionic conductance. The results showed that the tion are 0.15, 0.29, and 0.46 for PPy in 5, 25, and 50% RH, respectively. Also, the t(ion) can increase from 0.12 to 0.22 in dry nitrogen after PPy was modified with polyethylene oxide (PEO). (C) 2002 Elsevier Science B.V. All rights reserved.