The efficiency of inactivation of bacteria at initial populations of 10²–10⁷ CFU/ml in water by UV radiation of KrCl excilamp at 222 nm with and without hydrogen peroxide has been studied. At populations of 102–10⁵ FU/ml the total inactivation of E. coli O157:H7 and S. aureus was achieved during 15 s of irradiation. The UV/H₂O₂ inactivation rate constants for B. subtilis and B. cereus were two times higher than those observed for UV treatment alone. No effect of H₂O₂ was observed at 107 CFU ml-1 for Bacillus sp. and S. pyogenes.