Laboratory measurements of the gas-phase hydrolysis of N2O5 are always preturbed by wall reactions. Their contribution could be quantified in a large double-walled teflon bag chamber by introducing HNO3 into the chamber and analysing its temporal evolution in the gas-phase at low and high relative humidities, and by varying the surface-to-volume ratio of the chamber. By fitting a model to the experimental results, a consistent set of rate coefficients for adsorption and desorption of HNO3 from the chamber walls could be obtained. The desorption is so slow that the gas-phase hydrolysis of N2O5 via the reactions N2O5+H2O→2HNO3 (k1=2.5⋅10-22 cm3molec.-1s-1) and N2O5+2H2O→2HNO3+H2O (k2=1.8⋅10-39 cm6 molec.-2 s-1) is influenced by wall effects to less than 5%. The importance of the gas-phase N2O5 hydrolysis in the troposphere is discussed. ¿ 1998 American Geophysical Union