We have used a three-dimensional (3D) chemical transport model (CTM) to investigate the effect of interannual meteorological variability on ozone at middle latitudes. The CTM is forced by UK Meteorological Office analyses, includes a simple parameterization of ozone photochemistry and perturbed chlorine chemistry on polar stratospheric clouds (PSCs) and has been integrated for six years (1991–97). The modelled time series of the O3 column for the Northern Hemisphere middle latitudes shows a significant year-to-year variation which we attribute to transport processes, since the model's chemistry is effectively the same in each year. The model calculates its lowest ozone during 1993. This follows the Mt Pinatubo eruption but in this calculation cannot be due to chemistry on the enhanced aerosol surface area. The model indicates a contribution of the Arctic polar loss to mid-latitude ozone depletion each year during springtime, its influence being seasonal and not accumulating through the years.