Limb infrared spectral measurements of the 9.6-&mgr;m mesospheric ozone airglow were made by the Cryogenic Infrared Radiance Instrumentation for Shuttle (CIRRIS-1A) during one flight of the space shuttle Discovery (April 28th to May 6th 1991). A significant difference between ozone nightglow and dayglow is observed. The measured spectrally integrated ozone &ngr;3 fundamental band radiance profile is used to retrieve the ozone (&ngr;3=1) excited state density. Modeled ozone (&ngr;3=1) vibrational temperatures are used to infer the total ozone density. Night and day ozone abundance profiles inferred from ozone 9.6-&mgr;m infrared spectral emissions and comparisons with photochemical model calculations are reported. The observed ozone abundance is significantly larger than predicted by the photochemical model. ¿ 1998 American Geophysical Union