We use the SAM II extinction profiles and the associated temperature profiles to determine the amount of denitrification of the winter polar stratospheres. We see clear evidence of the denitrification process in the Antarctic data. There are indications in the Arctic data that denitrification mechanisms may be at work there also. At the latitudes observed by the SAM II satellite system, denitrification begins before the formation of extensive ice clouds and may be due to sedimentation of nitric acid particles. However, we cannot exclude the possibility of denitrificaiton by type II PSC's at latitudes not observed by SAM II. ¿ American Geophysical Union 1990