Tests carried out on eutrophic waters using ozone and peroxone (peroxide and ozone) indicated that an applied ozone concentration of between 1 and 1.5 mg/l (ozone:DOC ratio of 0.2 to 0.5) was generally required before significant removals of natural organic matter surrogate parameters and micropollutants were obtained. Peroxone produced the same effect as ozone used alone, but the maximum effect occurred at a lower ozone concentration when using peroxone. Peroxide to ozone ratios greater than 0.3 to 0.5 were not found to increase the benefit derived from the addition of peroxide.