An analysis has been carried out of the experiment of Norrish and Neville (1934) on ozone destruction in photolyzed Cl2-O3 mixtures. The experimental data can be quantitatively modeled by using reactions which are known to occur, and the analysis yields reaction rate information. In particular, the reaction of ClO with O3 is found to proceed at a rate of 8¿1019 cm3/s at 300¿K, the products being almost entirely ClOO+O2 or Cl+202. The implications of this analysis on concentrations of ClOO, OClO, and higher oxides of chlorine in the stratosphere are discussed.