Thermal emission from three rotational lines of H35Cl and H37Cl was observed with a Fourier transform spectrometer from a balloon platform at 28.9 km. The measured HCl line-of-sight density at 1.9¿ elevation above 28.9 km is 4.7¿1.3¿1015 cm-2, implying an average volume mixing ratio of 0.8¿0.2¿10-9 at the mean sampling altitude of 32.5 km. For a uniform mixing ratio model, this corresponds to a vertical column density of 2.4¿0.6¿1014 cm-2. Our result is in reasonable agreement with near infrared spectroscopic determinations and an abundance from a chemical sampling technique of HCl at this altitude; a pressure modulator radiometer measurement yields a significantly higher amount of HCl.