Multi-isotope (Δ17O and Δ18O) measurements of stratospheric CO2 and 14CO are reported. Samples were acquired from altitudes in excess of 11.5 km from Christchurch, New Zealand to the South Pole. A mass independent isotopic variation is observed in CO2, the magnitude of which correlates well with 14CO concentration, indicating a stratospheric source of the effect. The component arises from isotopic exchange between the product of O3 photolysis, O(1D) and CO2 thus providing a unique measure of ozone photolysis and turnover. A similar process may occur in the Martian atmosphere, as suggested by water isotopic measurements from SNC meteorites. ¿ American Geophysical Union 1995