Forty-three vertical profiles of ozone and temperature were measured at McMurdo Station, Antarctica, from 23 August to 1 November 1991. The data showed severe ozone depletion, during the springtime, for the third consecutive year. The lowest total column ozone, 146 DU on 10 October, was equal to the minimum measured in 1990, while the 18¿1 km ozone mixing ratio on this day was 0.1 ppmv, a factor of 2 below the previous minimum observed at this altitude. Most of the ozone depletion was once again confined to the 12--20 km layer, where an 83% reduction (105 DU to 18 DU) was observed, although there were also signs of depletion occurring in the 24--30 km region and below 12 km. Intrusions of ozone-rich air above 20 km caused substantial increases in total ozone during two periods when McMurdo was near or within the polar vortex wall. ¿ American Geophysical Union 1992