Global measurements of total column ozone from five inter-compared satellite-based instruments were used to calculate the daily global mass of ozone from November 1978 to December 1998. Missing data in polar darkness were estimated by interpolation across the polar caps. Global ozone mass and ozone mass totalled over 30¿ latitude zones were examined for the mean annual cycle, its evolution over the 20 year period, the impacts of volcanic eruptions and hemispheric differences in these impacts. Ozone mass for the globe or within a latitude zone is more suitable than mean column amount (e.g. in Dobson Units) because it is invariant under transport within zones and is a direct measure of exchange between zones. Furthermore, the relative contribution of impacts at different latitudes to global changes in ozone can be more easily quantified. While global ozone mass is significantly perturbed by high latitude wintertime ozone depletion, the impact of the Mt. Pinatubo eruption on northern midlatitude ozone mass was larger than any single Antarctic ozone hole event. ¿ 2001 American Geophysical Union