The concentrations of bacteria and moulds in the air decreased to undetectable levels in experiments with ozone and UV radiation. When exposed, in all of the species tested, viability on surfaces varied depending on the concentration and species of micro-organisms. At a concentration of less than 50 cm Ϫ2 , all species of micro-organisms were susceptible to the ozone and UV treatments at the laboratory table. At the concentration of 10 5 cm Ϫ2 , the most effective was ozone for Escherichia coli and Pseudomonas aeruginosa, while Bacillus subtilis was relatively more resistant. Compared with ozone treatment, the application of UV radiation was less effective on micro-organisms including methicillin-resistant Staphylococcus aureus when the micro-organisms were placed under the laboratory table.