Almost 20 years after Nicolet1 suggested the presence of nitric oxide in the upper atmosphere as a source of D-region ionization by solar Lyman α-radiation, this trace species was first observed2 by the resonance fluorescence method; almost 10 years later, its vertical distribution was observed in the stratosphere by means of balloon-borne infrared absorption spectrometry3. Since then much emphasis has been placed on odd nitrogen compounds in the stratosphere, partly because of their role in controlling the ozone abundance. Many measurements have been made of NO, NO 2, HNO3 and NO3 in the stratosphere with inferences on the N2O5 abundance. Meanwhile, several determinations of NO in the mesosphere and in the lower thermosphere 4-10 have used resonance fluorescence and mass spectrometry 11. We report here the first observation of NO from the low thermosphere down to the low stratosphere by instrumentation similar to that used previously on board balloon gondolas, but on this occasion the observation platform was Spacelab I, which gave access to higher altitudes. As before 12, NO and NO2 were observed simultaneously.