Aeronomers have generally admitted that the abundance of nitric oxide is small in the chemosphere. Its detection and even more its measurement have been regarded as a difficult task. The importance of this species in atmospheric chemistry, however, makes the effort to measure it worthwhile. Data have been obtained up to now by using the resonant scattering of solar ultraviolet radiation1 and the ionizing blunt probe technique2 in the mesosphere and lower thermosphere. Here we report the first determination of the vertical distribution of the abundance of nitric oxide in the stratosphere. The method involves absorption spectrometry in the 5.2 μm band of NO using the setting Sun as a light source.