Poly(pyrrole) (pPy) and poly(N-methylpyrrole) (pNMePy) films that were electrodeposited under similar conditions were compared in terms of electronic conductivities and counterion diffusion coefficients, Films were prepared and compared both in aqueous electrolyte (Cl-, ClO4- counterions) and in non-aqueous (propylene carbonate) electrolyte (ClO4- counterion). Consistent with the range of values reported in the literature, the electronic conductivities differed by a factor of ca, 5x10(3), although this is lower than the often-cited value of 10(5). This smaller difference in the conductivities is more consistent with that expected on the basis of simple steric factors. A.c. impedance measurements were used to determine the counterion diffusion coefficients. That for ClO4- was approximately one order of magnitude lower in pNMePy than that in pPy, possibly due either to differences in morphology or to stronger interactions of the counterion with the polymer chains.