Simultaneous, in situ measurements of OH, HO2, H2O, and O3 from 37–23 km are reported. The partitioning between OH and HO2 and the total HOx concentration are compared with expected steady‐state values. The ratio of HO2 to OH varies from less than 2 at 36 km to more than 3 at 25 km; in the lower stratosphere this ratio is nearly a factor of two less than predicted. The data are used to calculate HOx production and loss rates. The measured HOx mixing ratio is consistent with production dominated by the reaction of O(1D) with H2O, and loss controlled by NOy below 28 km and HOx above 30 km. The steady‐state concentration of H2O2 is inferred from the measured HO2 concentration and calculated photolysis rate. The maximum H2O2 mixing ratio (at 33 km) is predicted to be less than 0.2 ppb.