Very large solar proton events (SPEs) occurred from October 19--27, 1989. These SPEs are predicted to produce short-lived increases in HOx and long-lived increases in NOx species, which both can lead to ozone destruction. December 1989 SBUV/2 measurements of upper stratospheric ozone show substantially more ozone depletion in the Northern than in the Southern Hemisphere even though the amount of HOx and NOx produced in both hemispheres should be similar from these SPEs. Our two-dimensional (2D) model simulations predict only a modest interhemispheric difference in the ozone depletion in December caused by the October 1989 SPEs. In an attempt to better understand the interhemispheric difference in the observed ozone depletion, we have used the GSFC three-dimensional (3D) chemistry and transport model to simulate the distribution of NOx and ozone after the SPEs. Our 3D model computations of ozone and NOx behavior for two months after the October 1989 SPEs indicate differences in the constituent behavior in the two hemispheres during the October-November-December 1989 time period which are qualitatively consistent with SBUV/2 ozone observations. These differences are caused by: 1) Substantial mixing of perturbed air in the Southern Hemisphere from the polar region with unperturbed lower latitude air during the November final warming; and 2) Significant confinement of the photochemically perturbed air in the Northern Hemisphere in the winter-time polar vortex. ¿ American Geophysical Union 1993