Conductivity measurement on films of acid-doped polybenzimidazole (PBI) was performed by impedance spectroscopy, A complete set of data for PBI-H3PO4 and PBI-H2SO4 complexes is reported as a function of temperature (30-90 degreesC) and isostatic pressure (1-4000 bars). Experimental results indicate an activated mechanism for the proton migration. Isobar and isothermal conductivity data allow the determination of the characteristic thermodynamic parameters DeltaV * (4-10 cm(3) mol(-1)). DeltaH * (0.6-1.1 eV) and DeltaS * (40-190 J mol(-1) K-1), The dependence of these parameters on temperature and pressure is consistent with thermodynamic predictions. Based on a previous IR spectroscopic study of PBI-acid complexes, a microscopic model is developed, suggesting proton transfer from one imide site to another in which the anionic species participate by a Grotthus mechanism.