The ozone altitude profile for 25≤z≤55 km was measured from McMurdo Station, Antarctica, by ground-based millimeter-wave spectrometry, on 34 days between September 12 and October 29, 1986. The mixing ratio peaked at altitudes ranging from 28 to 34 km, with peak values between 5 and 9 parts per million by volume (ppmv). The ozone mixing ratio at 25 km decreased by 15¿5% (1&sgr; uncertainty) during the period. No significant decrease was observed at higher altitudes; the upper limit on any secular trend at 33 or 40 km is ~8%. Considerable variability, was observed at all altitudes, on time scales of 1 to a few days. In the most dramatic case, ozone in a layer 25≤z≤40 km nearly doubled between September 20 and 23. This was accompanied by a significant warming and an increase in N2O at the same altitudes. We compare our results to concurrent balloonsonde ozone measurements, to a model prediction, and, by combining our results with the balloonsonde profiles, to satellite measurements of total ozone. The observation that ozone depletion was confined to the lower stratosphere is consistent with theories invoking heterogeneous chemistry associated with polar stratospheric clouds. It may be consistent with theories which predict upwelling of ozone-poor air, if such upwelling is confined to the lower stratosphere. Our data do not support theories predicting depletion in the upper stratosphere, but the seasonal coverage of the measurements was too limited to be definitive. ¿ American Geophysical Union 1987