The simultaneous deposition of W(VI) and Co(II) species on the gamma-alumina surface from aqueous solutions has been studied. Mutual promotion in the deposition of W(VI) and Co(II) species was observed due to the strong lateral attractions exerted between the codeposited W(VI) and Co(II) species. A model was developed according to which the deposition of cobalt takes place through the adsorption of one Co2+ ion at a site created by one deprotonated surface hydroxyl, whereas the deposition of tungsten takes place mainly via adsorption of the WO42- and HW6O20(OH)(2)(5-) ions at sites created by the protonated surface hydroxyls. The adsorbed WO42-[HW6O20(OH)(2)(5-)] ions increased [decreased] with increasing pH. The total tungsten (cobalt) deposited decreased (increased) with increasing pH.