A method to compute the optical indices of a thin absorbant film, together with those of its metallic substrate, from a statistical analysis of the reflectance changes with film thickness d of the metal-film system is given. The results are applied to anodic oxide films grown on titanium. The accuracy of the indices of the titanium substrate is shown to be a function of the ratio of the film thickness to the wavelength. By using films with thicknesses ranging between 10 and 2500 Å, the optical indices in a wavelength range 0.25–2.5 μm were obtained. The titanium indices are compared with results recently cited in the literature; the accuracy of our result, for instance in the determination of the bulk plasmon frequency, is demonstrated.