During the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and ValidationExperiment (SOLVE)/Third European Stratospheric Experiment on Ozone (THESEO) campaign,Polar Ozone and Aerosol Measurement (POAM) III sampled in the vortex core, on the vortexedge, 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, ozonemixing ratios in the core of the vortex dropped from about 3.5 ppmv in mid-January to about 2ppmv by mid-March at 500 K. The ozone chemical loss indicated by these measurements isassessed using two methodologies. First, the POAM data is used to construct vortex-averagedozone profiles, which are advected downward using vortex average descent rates. The maximumozone loss (1 January to 15 March) is found to be about 1.8 ppmv. In a second approach, theREPROBUS 3-D CTM is used to specify the passive ozone distribution throughout the winter. Thechemical loss in the vortex is estimated by performing a point-by-point subtraction of the POAMmeasurements inside the vortex from the model passive ozone evaluated at the time and locationof the POAM measurements. Both ozone loss estimates are in general agreement and they agreewell with published loss estimates from ER2 and ozonesonde measurements.