The uptake of HBr in water ice has been investigated in a flow reactor under polar atmospheric conditions. The HBr uptake on ice films was determined in the range of 1.1¿0.7¿1014--7.7¿1.1¿1016 molecules/cm2 at 188 and 195 K as HBr partial pressures varied from 3.7¿10-8 to 6.4¿10-6 Torr. This is the first report of a laboratory study at polar atmospheric conditions that shows HBr⋅3H2O to be formed during the uptake process. The HBr adsorption and uptake thermodynamics were also investigated. The implications of these new findings for the heterogeneous chemistry of the polar ozone depletion are briefly discussed. ¿ American Geophysical Union 1995