Model aq. 100-mg/L Acid Violet 1, Reactive Blue 13, Direct Blue 74, or Reactive Orange 20 solutions were decolorized, 90-100% in 5-10 min, with 15 L/h air-O-3 produced at 20degreesC in a 4 g O-3/h ozone generator. Redox potential, 350380 mV for 9-10 min, jumped on the 10(th) min to similar to1000 mV Diffusion of Q, from the gas into the water phase was the controlling step. Dye reactivities descended in the order of the dyes given above. With 1 mg H2O2/mg dye and 5 mg/L FeCl2 as catalyst, pH 3.5, 20degreesC, 80% and >98% decolorizations took 10-20 and 45-60 min, resp. Direct Blue 74 was most resistant and required 60degreesC. Ozone was superior to H2O2 as oxidant.