The spectral emission of the lower stratosphere in the far infrared region (100–140 cm −1) has been measured with a high resolution (0.02 cm −1) Michelson interferometer from the Gerard P. Kuiper Airborne Observatory flying at 13 km altitude. The observed spectra are compared with synthetic emission spectra in order to perform the line assignment. Most of the lines in this spectral range are due to the major atmospheric absorbers (H 2 16O, O 2, O 3). The measured line frequencies, for these constituents, are in excellent agreement with their predicted values (within 0.005 cm −1). A number of lines have been attributed to HDO, H 2 17O and H 2 18O and their measured frequencies are listed. A few observed lines remain unassigned and are not thought to be due to the above constituents or to CO, N 2O and NO whose lines are included in our synthetic spectra.