The combination of different in situ techniques allows a more complete analysis combining several physical and chemical processes of polymer-modified electrodes to be obtained. The hybrid technique -cyclic electrogravimetry coupled with visible-near infrared spectroscopy- was used to study in depth the electrochemistry of poly(o-toluidine) (POT) thin films. In this work, a POT modified electrode was polarized between the pernigraniline and leucoemeraldine forms in 0.5 M HNO3 and 0.5 M HClO4 solutions. The electrochromic properties of View the MathML sourcePOT-CIO4− and View the MathML sourcePOT-NO3− were localized in the experimental potential range associated to the transfer of charged species during the redox reactions. The analysis of all the experimental results has allowed the main contribution of proton, anion and water transfers to be separated in three redox transitions together with the electrochromic properties of POT. Semi-quantitatively, the better electrochemical and electrochromic properties of both films take place predominantly at potentials where the higher accumulation of the radical cations (polarons and bipolarons) in the polymer structure involves great lattice reorganization. The analysis of this work is a complete objective manner to discriminate the better conditions where a film can be used for a specific technical application.