Variable angle spectroscopic ellipsometry was employed for multilayer characterization of thermally oxidized porous silicon layers and for quantitative adsorption studies of human serum albumin and fibrinogen in these layers. The oxidized samples were used either as prepared or were hydrated in a deionized water bath prior to their use. Hydration decreased the volume percentage of adsorbed albumin from 24 to 13% in the sublayer next to the ambient but resulted in an increase of the amount of adsorbed protein deeper in the film. Hydration did not, however, affect the adsorption behavior of fibrinogen which was found to adsorb only in the outermost sublayer. This phenomenon was attributed to the larger size of this protein. The amount of adsorbed fibrinogen depended on the concentration of the protein in the stock solution.