Measurements of the concentration profiles of key stratospheric reactive, reservoir and source gases, ClO, O3, HCl, N2O and CCl2F2, were made during two balloon flights in the Arctic on 27 January and 08 March 1995 that were part of the Second European Stratospheric Arctic and Mid-latitude Experiment (SESAME). On 27 January, low abundances of HCl (~250 ppt at 50 hPa) were measured in air parcels that had been at temperatures below the type I PSC existence threshold accompanied by high concentrations of ClO (1.6 ppb at 50 hPa). Calculations using the currently recommended photochemical data yield a ratio of [ClO>+2[Cl2O2>+[HCl> to [Cly> near unity in these air parcels. The 08 March flight sampled warm stratospheric conditions outside the vortex with normal mid-latitude ClO (<100 ppt at 50 hPa) and HCl abundances comprising about half of the available chlorine at 50 hPa. ¿ 1999 American Geophysical Union