Measurments of ozone, water vapour, nitric acid and nitrogen dioxide taken during the STRATOPROBE flight of October 23, 1980 from Palestine Texas at 32¿N are presented. The measured ratio of HNO3 to NO2 is in good agreement with that of a one dimensional model using current photochemistry. The measured ratio is used to infer ''proxy'' hydroxyl densities. These OH densities are very low below 25 km, in agreement with the findings of earlier flights.