The influence of pH changes on potentiometric responses of poly(pyrrole) films was studied. In our opinion three effects have to be considered, namely: (i) the participance of H + in ion exchange processes on the polymer/solution interface, (ii) protonation/deprotonation of the polymer film and (iii) redox side reactions between the polymer matrix and solution components, in which H + ions are involved. The results obtained indicate that the effect of solution redox potential, which is pH dependent, and protonation of the film are important factors affecting potentiometric responses of poly(pyrrole) in moderately acidic media.