The effects of sulfate aerosols on stratospheric ozone have been studied with a 2D model. The model includes a comprehensive chemical code for homogeneous and heterogeneous reactions; both background and volcanic aerosols have been taken into account according to different scenarios. The basic temperature field is prescribed, while the perturbation introduced by the presence of volcanic aerosols is predicted. Increase of total chlorine in the stratosphere causes a well known ozone depletion by itself, but the effects could be highly enhanced in presence of a large amount of volcanic aerosols that affect the balance of nitrogen and chlorine reservoirs through heterogeneous chemical reactions. For a volcanic eruption similar to El Chich¿n we show that the maximum O3 depletion (7% for a 2.5 ppbv amount of stratospheric chlorine and 12% by doubling Cl) is to be expected at high latitudes in spring, because of a large chemical destruction acting in situ. ¿ American Geophysical Union 1991