During the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE)/Third European Stratospheric Experiment on Ozone (THESEO) campaign, Polar Ozone and Aerosol Measurement (POAM) III sampled in the vortex core, on the vortex edge, and outside the vortex on a near-daily basis from December 1999 through mid-March 2000. During this period, POAM observed a substantial amount of ozone decline. For example, ozone mixing ratios in the core of the vortex dropped from about 3.5 ppmv in mid-January to about 2 ppmv by mid-March at 500 K. The ozone chemical loss indicated by these measurements is assessed using two methodologies. First, the POAM data is used to construct vortex-averaged ozone profiles, which are advected downward using vortex average descent rates. The maximum ozone loss (1 January to 15 March) is found to be about 1.8 ppmv. In a second approach, the REPROBUS 3-D CTM is used to specify the passive ozone distribution throughout the winter. The chemical loss in the vortex is estimated by performing a point-by-point subtraction of the POAM measurements inside the vortex from the model passive ozone evaluated at the time and location of the POAM measurements. Both ozone loss estimates are in general agreement and they agree well with published loss estimates from ER2 and ozonesonde measurements.