Differential electrochemical mass spectrometry (DEMS) and Fourier transform infrared spectroscopy (FTIRS) are used to provide evidence of the existence of a free metal surface under electrodeposited polyaniline (PANI) films. With this purpose, both methanol oxidation and CO adsorption are studied on Pt electrodes modified by electrodeposited polyaniline films (PANI/Pt). Using the DEMS signal for CO2 (m/z = 44) to follow the oxidation of adsorbed CO to CO2, the exposed Pt surface area under the film is evaluated to reach similar to30% of the clean Pt electrode. CO adsorption on a PANI/Pt electrode is clearly detected by FTIRS through the bands at 2080 and 1820 cm(-1) for linear and bridge bonded CO, respectively. The free area seems to behave differently than clean Pt toward methanol oxidation. The in-situ FTIR spectra present only a band at 2343 cm(-1) due to CO2 formation, but not those due to CO adsorption, suggesting a change in the oxidation mechanism.