Measurements of ClO over Antarctica during the 1996 to 2000 ozone holes are compared with predictions of the SLIMCAT model. The model captures all of the major features of the measurements, including the rapid rise in August, the drop in mid or late September due to the arrival of warmer, ClOx poor air overhead, and the deactivation of ClOx into the reservoir species, HCl and ClONO2 in the ozone poor air. The model uses the standard JPL rates for the photolysis of the ClO dimer (j) and for the forward reaction forming the dimer (kf). The predicted ClO mixing ratios and columns are in excellent agreement with the measurements. A comparison of the model and data for all 5 years leads to a value of the ratio (j/kf) consistent with the standard value, namely 1.06 ¿ 0.30(j/kf)JPL.