Upper stratospheric photochemical lifetimes are estimated in situ for CH4 and N2O for the first time, based on an analysis technique using 3 years of satellite measurements from the Stratospheric And Mesospheric Sounder (SAMS) instrument. The technique involves investigation of the time dependence of tracers injected into high Northern latitudes in late winter and their subsequent photochemical decay during the dynamically quiescent summer stratosphere. Dynamical corrections are made for mean meridional circulation contributions. The lifetimes for N2O at 2 and 7 hPa(~43 and ~35 km altitude) are found to be 1.7 and 8.3 months, respectively. For CH4, 0.6 (~52 km altitude) and 2 hPa lifetimes are 3.3 and 3.4 months, respectively. These observed values are in good agreement with model calculations by Solomon et al. [1986>. ¿American Geophysical Union 1991