Simultaneous balloon-borne observations of ozone (O3) and nitrous oxide (N2O), a long-livedtracer of dynamical motion, are used to quantify the chemical loss of ozone in the Arctic vortexduring the winter of 1999/2000. Chemical loss of ozone occurred between altitudes of about 14 and22 km (pressures from ~120 to 30 mbar) and resulted in a 61 ± 13 Dobson unit reduction in totalcolumn ozone between late November 1999 and 5 March 2000 (the date of the last balloon-bornemeasurement considered here). This loss estimate is valid for the core of the vortex during the timeperiod covered by the observations. It is shown that the observed changes in the O3 versus N2Orelation were almost entirely due to chemistry and could not have been caused by dynamics. Thechemical loss of column ozone inferred from the balloon-borne measurements using the "ozoneversus tracer" technique is shown to compare well with estimates of chemical loss found usingboth the Match technique (as applied to independent ozonesonde data) and the "vortex-averageddescent" technique (as applied to Polar Ozone and Aerosol Measurement (POAM) III satellitemeasurements of ozone). This comparison establishes the validity of each approach for estimatingchemical loss of column ozone for the Arctic winter of 1999/2000.