Mixing ratios of the conserved tracers SF6 and CO2 in air samples collected with cryogenic whole-air samplers during two balloon flights in the Arctic and mid-latitude stratosphere up to 30 km altitude in 1997 are presented. The data are used to derive the mean age of stratospheric air. The calculated CO2-ages agree with the corresponding SF6-ages to within 0.5 years. These results do not confirm the findings previously reported by Harnisch et al. [1998> but rather suggest that SF6 and CO2 can be regarded as equivalent age tracers. However, evidence is presented that this general agreement may not be valid for polar stratospheric air parcels that comprise fractions of mesospheric air. ¿ 2000 American Geophysical Union