A modified iodometric procedure using an absorbing solution of 2% NBKI with a known amount of As(III) is described for 10 ml aqueous samples. Ozone contents from 0.5 to 65 mg O3/I were determined. High ozone concentrations can also be measured for generator calibration. This method gives results which are not significantly different than a boric acid method but are for a modified standard methods procedure. Volatility of iodine has been completely eliminated. Stabilized samples do not make the time between sampling and final titration critical.