Infrared atmospheric absorption spectra at ~0.02 cm-1 resolution obtained during a balloon flight made on March 23, 1981, show absorption features attributable to C2H2. These features are used to derive a preliminary mixing ratio of ~25 pptv near 9 km. This mixing ratio falls into the range of values we calculate for upper tropospheric C2H2 in a photochemical/transport model but well below values measured previously in samples collected by other researchers.