Correlations between deviations from mean profiles of CH4 and N2O vertical distributions in the stratosphere and air mass trajectories in the 100 mbar and 30 mbar level are discussed. The profiles wre taken from results of 11 balloon flights over France and 3 flights over Laramie/Wyoming during 1976--1980. The deviations in the proifles appear to depend on the origin of the air masses. Compared with the results from the lower stratosphere, the conditions in the middle stratosphere between 20 and 36 km height are more complex and seasonally dependent. Some possible explanations with respect to the general circulation in the stratosphere and troposphere are given.