Mass spectrometer measurements of ozone made during two balloon flights included its heavy isotopes at mass 49 and 50. Both flights were flown during the day and during summer from Palestine, TX. At float altitudes above 42 km the enrichments in heavy ozone were 41% and 23%, respectively. The enrichment appears to be mass independent since, at high altitudes, both 49 and 50 show the same enhancement. During the descent the enrichment in heavy ozone decreased, faster during the first flight than during the second, reaching values between 15 and 20% above 30 km. Near and below this altitude another increase is observed. During a night flight, previously reported, an enhancement in heavy ozone of over 40% at 32 km was found, decreasing both toward higher and lower altitudes. ¿ American Geophysical Union 1987