Atmospheric O3 mixing ratios measured by ILAS and HALOE are compared for periods from March 25--31, 1997 in the NH and from November 20--24, 1996 and December 13--14, 1996 in the SH. Both instruments observe consistent vertical and horizontal structure in the highly variable polar vortex regions. In the ozone peak region, ILAS ozone values are smaller compared to HALOE values in both hemispheres, but the differences are less than 13% and 20% in 40-20 km altitude range, respectively, for the NH and the SH, which are both close to the sum of uncertainties of the two instruments. When validation is complete, ILAS data will be useful for the study of the chemistry and dynamics at high latitudes. ¿ 1999 American Geophysical Union