ClO has been detected in the stratosphere from observations of the solar spectrum in the infrared, in a small spectral interval near 12 &mgr;m. The observations were made with a balloon-borne laser heterodyne radiometer, launched from Palestine, Texas on September 20. By comparing high sun spectra with a number of sequential spectra taken during sunset, an altitude profile has been calculated in the 29--38 km altitude range. The results show a peak mixing ratio in excess of one ppb above 34 km, and a rapid decrease in mixing ratio with decreasing altitude below 34 km.