The rate of loss of ClO on Pyrex, water ice, and nitric acid trihydrate, NAT, surfaces at 183 K has been measured in a flow reactor sampled by a mass spectrometer. Upper limits for the rates of loss of ClO on Pyrex at 295 K, Cl2 on ice at 183 K, and O3 on Pyrex, ice, and NAT surfaces at 183 K have also been determined. In all cases the probability of loss of the species from the gas-phase upon collision with the surface is less than 10-4. These small values make it probable that heterogeneous reactions involving these species are unimportant in the winter polar stratosphere. ¿ American Geophysical Union 1993