The formation of a radical cation, by electrochemical oxidation of the neutral red dye in acidic aqueous solution, is controlled by diffusion towards the electrode surface. This is the initiation step of the electrogeneration, potentiostatic or potentiodynamic, of poly(neutral red) films on an indium-tin oxide (ITO) electrode. The polymeric film is a redox semi-conductor, and shows a microporous membrane-like character. Its electrochemical behaviour depends on the generation process. The hydrogen ions play a double role : first as reactants at electrochemical and acid-base equilibrium, second as counterions of the electrons. The global process of the electron-hopping is limited by the low electronic conductivity of the material. In spite of this, the thin films deposited on the ITO electrode can act as a pH potentiometric sensor.