The partitioning of the active nitrogen and chlorine families (NOy,Cly) between 24 and 32 km and 30¿ and 75 ¿N in summer and autumn is studied using a photochemical box model. Data obtained from the Halogen Occultation Experiment (HALOE) are used to initialize the model and to obtain measured values for NO, NO2 and HCl. When the recommended kinetic and photochemical parameters are used, the model underestimates the NOx/NOy ratios by 15--35%. As in analyses of aircraft, balloon, and laboratory data, it is found that the gas-phase processes which link NOx and HNO3 are inadequately represented by the model. The inclusion of rate expressions derived recently for the reactions of OH with NO2 and OH with HNO3 in the model results in 8--20% increases in NOx, where the larger increases are obtained at lower altitudes. Despite better agreement resulting from the use of new rate expressions, differences in excess of 20% remain between NOx/NOy values obtained from measurements and calculations. The remaining differences are particularly noticeable above about 27 km. This implies that further studies of the reactions controlling partitioning in the NOy family are necessary. The use of branching ratios determined recently for the production of HCl from the reaction between ClO and OH leads to better agreement for the HCl/Cly ratios obtained from measurements and calculations for altitudes above 27 km. However, the agreement below 27 km becomes poorer as a result of calculated additional production of HCl. Overall, within the recommended uncertainties for the relevant rate coefficients, the model predictions for HCl/Cly agree with the values obtained from measurements between 24 and 32 km. ¿ 1999 American Geophysical Union