The rate constant for the reaction ClO + NO2 + M has been measured between 150 and 600 Torr and at 298 and 213 K using a turbulent flow technique with high-pressure chemical ionization mass spectrometry for the detection of reactants. This work represents the first experimental evaluation of this rate coefficient at temperatures below 248 K. The results are in excellent agreement with the values recommended by the NASA Panel for Data Evaluation (DeMore et al., JPL Publication 97-4, 1997).