Ozone isotope data for 49O3 and 50O3 are presented, that were obtained from 28 stratospheric samples collected over 10 years on board balloon payloads. Enrichments for 49O3 range from 7 to 9% in the middle stratosphere. This is in very good agreement with laboratory-derived isotope predictions. For 50O3 most enrichments are between 7 and 11%, a few, however, are too high to be of atmospheric origin. Arguments are presented that stratospheric ozone isotope data are consistent with enrichments determined in laboratory studies when pressure and temperature dependence of the isotope effect is included. Results from recent remote sensing experiments support the values obtained during balloon-borne sample collections. Very high enrichments occasionally measured in the past should be disregarded. ¿ 2001 American Geophysical Union