X-ray photoelectron spectroscopy (XPS) was used to determine changes in titanium oxide composition, oxide stoichiometry, and adsorbed surface species as a function of exposure to model physiologic environments. The oxide on titanium became heterogeneous and polarized as a function of exposure. Changes included an increase in surface hydroxyl groups, and adsorption of H2PO4- and HPO4(2-). The heterogeneous nature of the surface led to preferential adsorption of lipoproteins, glycolipids, or both from serum.