The electroreflectance technique was applied to the case in which a thin dielectric film is present at a metal-electrolyte interface. The Ti/TiO2H2SO4 system, in which an optical response characteristic of the TiO2 film properties could be obtained for films with thicknesses of about five monolayers, was investigated experimentally. Photocurrent spectra were also obtained and information relevant to the properties of the very thin films was determined by a combination of these two optical techniques.