Fundamental band emission from the v=1 levels of isotopically substituted 13C16O and 12C18O has been observed for the first time in the earth's atmosphere. High-resolution earthlimb spectra were obtained in the Cryogenic Infrared Radiance Instrumentation of Shuttle (CIRRIS 1A) experiment under both nighttime and daytime conditions. Spectral data between 70 and 150 km tangent height were analyzed in the 4.7 &mgr;m wavelength region, providing absolute 12C16O, 13C16O, and 12C18O column radiances. The minor isotope column radiances are up to 30 times more intense than predicted, based solely on the natural isotopic abundances of 13C and 18O. The derived line-of-sight radiances were accurately modeled using the Phillips Laboratory Atmospheric Radiance Code, and provide a strong test of radiative transport and excitation algorithms, as well as model climatologies. ¿ American Geophysical Union 1993