The infrared emission spectrum of the upper atmosphere between 1.2 and 2.5 microns has been measured at night by means of a Michelson interferometer carried to an altitude of 90,000 feet by a balloon. The complete Δν = 2 sequence of rotation–vibration OH bands has been observed at a resolution sufficient to resolve the rotational structure. The (0, 0) band of the electronic transition [Formula: see text] of oxygen at 1.27 microns has been observed in the night-sky spectrum for the first time. Its brightness is comparable with that of the (4, 2) OH band at 1.6 microns.