Model calculations suggest that the ozone decrease observed a few years after the eruptions of Mt. Pinatubo and El Chichon may have been unique in the Earth's history, and is directly linked to the emission in the atmosphere of industrially manufactured chlorofluorocarbons. For chlorine loadings typical of the pre-1980 period, the ozone column abundance should have increased after a large volcanic eruption. After 1980, as a result of growth in chlorine loading, the response of ozone became negative in winter at mid- and high latitudes. In the future, the response of ozone is expected to become positive again, if the production of chlorofluorocarbons is sufficiently reduced. The calculations also show that, under low chlorine loadings, the response of ozone is insensitive to the magnitude of the eruption, while, under present conditions (high chlorine loading), the ozone depletion increases with the amount of SO2 injected in the stratosphere by the volcano. ¿ American Geophysical Union 1995