Simultaneous balloon-borne observations of ozone (O3) and nitrous oxide (N2O), a long-lived tracer of dynamical motion, are used to quantify the chemical loss of ozone in the Arctic vortex during the winter of 1999/2000. Chemical loss of ozone occurred between altitudes of about 14 and 22 km (pressures from ~120 to 30 mbar) and resulted in a 61 ¿ 13 Dobson unit reduction in total column ozone between late November 1999 and 5 March 2000 (the date of the last balloon-borne measurement considered here). This loss estimate is valid for the core of the vortex during the time period covered by the observations. It is shown that the observed changes in the O3 versus N2O relation were almost entirely due to chemistry and could not have been caused by dynamics. The chemical loss of column ozone inferred from the balloon-borne measurements using the ozone versus tracer technique is shown to compare well with estimates of chemical loss found using both the Match technique (as applied to independent ozonesonde data) and the vortex-averaged descent technique (as applied to Polar Ozone and Aerosol Measurement (POAM) III satellite measurements of ozone). This comparison establishes the validity of each approach for estimating chemical loss of column ozone for the Arctic winter of 1999/2000.