Isotope ratios of stratospheric ozone samples collected during four balloon flights are reported. In an altitude range between 22 and 33 km all ratios show enrichments between 7 and 11%, somewhat lower for 49O3 than for 50O3. Those enrichments are in very good agreement with results from laboratory isotope studies when stratospheric pressure and temperatures are included. The new data presented do raise questions about past stratospheric ozone isotope measurements which sometimes showed high values never observed in the laboratory or tropospheric environment. ¿ 2000 American Geophysical Union