Under natural sunlight (975 +/- 25 Wm(-2)), CeO(2) catalyzes the oxidation of cyanide to cyanate in alkaline medium and the photokinetic behaviour of the reaction is similar to those on TiO(2) and ZnO surfaces; the oxidation follows the Langmuir-Hinshelwood kinetics on cyanide ion, and depends on the area of the catalyst bed and dissolved oxygen. However, the adsorption of cyanide on the oxides in dark is too small to be measured analytically and detected spectroscopically. Although the photocatalytic efficiencies under identical solar irradiance are of the order: CeO(2) < ZnO < TiO(2), which is in accordance with the charge-transfer resistance and capacitance of the oxides. CeO(2) and ZnO show bactericidal activity as well. At a loading of 0.8 gL(-1) they inactivate 40 and 44% of 2.5 x 10(12) CFU mL(-1) E. coli in 30 min even without direct light.