Methyl nitrate has been measured for the first time in the lower stratosphere at altitudes to 20.5 km during the December 1996 NASA Stratospheric Tracers of Atmospheric Transport (STRAT) deployment. Whole air samples were taken on board the NASA ER2 aircraft and analyzed using gas chromatography/mass spectrometry. Methyl nitrate was present at measurable levels throughout the entire altitude range covered. Taking advantage of the rather simple chemistry in the lower stratosphere compared to the troposphere, and considering the known in-situ photochemical sources for methyl nitrate, the yield of methyl nitrate from the reaction of methyl peroxy radicals with NO was estimated. ¿ 1998 American Geophysical Union