During the period from August 25 to November 3, 1986, the r ≧ 0.15 μm and r ≧ 0.25 μm aerosol profiles were measured on six occasions at McMurdo Station (78°S) by balloon‐borne optical particle counters. In addition, condensation nuclei (r ≧ 0.01 μm) profiles were measured on three occasions between October 16 and November 3. Several of these measurements corresponded to times when McMurdo was located near the point of minimum springtime ozone, as indicated by ozone and temperature measurements conducted on 33 occasions during the period. The height of the stratospheric sulfate layer was observed to decrease over the period of measurement, indicating continued subsidence in the vortex during the period that ozone was decreasing. This observation suggests that upwelling in the vortex is not important in the ozone depletion process. Low concentrations of condensation nuclei in the region of the ozone minimum supports this conclusion. Enhanced condensation nuclei above 20 km in the vortex and the discovery of an apparent permanent layer in the springtime vortex at the top of the ozone depletion region suggests that they may be related to the ozone depletion process, although the nature of this relationship i