The rotational transitions J=35/→33/2 and J=37/2 35/2 of 35CIO at 21.663 cm-1 (649.45 GHz) and 22.898 cm-1 686.45 GHz), respectively, have been identified in stratospheric emission spectra measured with a limb-sounding Fourier transform spectrometer during ballon flights in April 1979 and October 1982. The measurements provide information on the ClO concentration at altitudes around 28 km. The fit of the observation with the theoretical ClO profile by Ko and Sze (1984) gives, in the case of the afternoon measurements obtained in 1979, a scaling factor of 0.85 (+0.67, -0.64), and in the case of the afternoon and early morning measurments obtained in 1982 flight, a scaling factor of 0.88 (-0.18, -0.08). A day to night variation is observed. ¿ American Geophysical Union 1988