Rate constants have been measured for the gas phase reaction of the hydroxyl radical (OH) with CH3Br over the temperature range 250 to 400 K. The Arrhenius expression k=5.79¿10-12 exp(-1560/T) cm3 molecule-1 s-1 was derived from the kinetic data. From the rate constant at 277 K, the tropospheric lifetime of CH3Br with respect to reaction with OH is estimated to be 2.2 years and the overall atmospheric lifetime to be 2.1 years. ¿ American Geophysical Union 1992