We report simultaneous measurements of the stratospheric concentration profiles of OH, HO2, H2O2, H2O, O3, HNO3, NO2, N2O, HCl, HOCl, and ClO during a midlatitude balloon flight in 1989. Measurements were made over almost an entire diurnal cycle by the Smithsonian Astrophysical Observatory Far-Infrared Spectrometer (FIRS-2) and the Jet Propulsion Laboratory Balloon Microwave Limb Sounder (BMLS). We analyze these measurements using a photochemical model constrained by observations of long-lived gases. Measured HOx species (OH and HO2) and H2O2 show fair agreement with theory throughout the diurnal cycle. Measurements of HNO3 are higher than theory near the concentration peak, while the levels of NO2 are consistent with the model at most altitudes. Measurements of ClO and HOCl are less than predicted concentrations, suggesting a source of HCl in addition to the reaction of Cl with CH4. Possibilities for such a source include a minor HCl+O2 product channel for the reaction of ClO with OH and a minor HCl+O3 channel for the reaction of ClO with HO2. ¿ American Geophysical Union 1996