Simultaneous measurements of NO3 and O3 were performed at different periods of the night from stratospheric balloons launched from the CHES balloon station at Aire-sur-l'Adour in September 1980 and September 1981. The experimental NO3 vertical profiles compare favorably with those predicted by the photochemical theory. Differences can be explained by the dependence of the recombination rate of NO2 and O3 upon altitude. The O3 concentrations above 30 km measured by spectrophotometry around λ=660 nm present a remarkable stability. Measurements obtained by means of this technique could be used as a reference for the detection of long-term variations of O3.