The Microwave Limb Sounder (MLS) observed ozone (O3) loss in the Arctic vortex beginning in January 1997 at 585 K (~25 hPa) and in February 1997 at 465 K (~50 hPa). Minimum vortex-averaged O3 mixing ratios observed in 1997 were higher than those in 1996, which were the lowest ever recorded by MLS. The vertical extent of O3 loss and maximum local O3 decreases were larger, but the decrease filled the vortex less completely, in 1997 than in 1996. Unusually low high-latitude column O3 above 100 hPa in April 1997 resulted mainly from dynamical effects of the unusually persistent lower stratospheric vortex and winter-like temperature patterns. Column O3 above 100 hPa averaged in comparable regions of the vortex showed a stronger decreasing trend in 1996--97 than in 1995--96, consistent with the larger vertical extent and maximum local values of lower stratospheric O3 loss. Chemical O3 loss resulted in an ~10% observed decrease in column O3 between late January and early April 1997. ¿ 1997 American Geophysical Union