We have measured the vertical profiles of several isotopomers of nitrous oxide, N2O, in the stratosphere by balloon-borne infrared remote sensing between 15 and 35 km. In particular we distinguish the individual profiles and relative enrichments of the positional isotopomers 15N14N16O and 14N15N16O for the first time. We find a distinct and reproducible relative enrichment of the isotopomers which is in general agreement with measured photolysis rates in the laboratory and theoretical predictions. The results confirm photolysis as the dominant stratospheric loss process for N2O and argue against suggestions that additional chemical sources of N2O in the stratosphere are required to explain the observed heavy isotopic enrichments there. ¿ 2000 American Geophysical Union