Observations made by the HALOE instrument aboard UARS show very low stratospheric ozone in the Arctic and Antarctic summers of 1992 and 1993 [Park and Russell, 1994>. Large longitudinal variability is seen in ozone between 8 and 45 mb, poleward of 60¿ during late summer. This paper examines the cause of this variability using isentropic trajectory analysis and photochemical calculations. According to trajectory analysis using UKMO wind fields, air parcels with higher ozone mixing ratios move to 73 ¿N from lower latitudes in the longitude sector 180 ¿E--225 ¿E over a 9 day period beginning on 10 August, 1993. Low ozone values seen in the HALOE data around 100 ¿E at 73 ¿N correspond to air parcels that remain mostly in higher latitudes. We present results from photochemical calculations conducted in conjunction with UARS data, and conclude that the longitudinal asymmetry in ozone can be explained by transport along isentropic trajectories with standard chemistry.¿ 1997 American Geophysical Union