Data from a chemiluminescent NO detector, and an in situ ozone instrument are presented. The measurements were made on September 17, 1987 and on June 18, 1988 aboard high altitude balloons launched from the French CNES Balloon Launching Center at Aire sur l'Adour (44¿N, 0¿W) and from Gap (44.5¿N, 6¿E). The NO measurements above 32 km are more accurate than previous determinations due to a more precise regulation of the sample flow rate at pressures down to 2 mb, with a reduced ozone/oxygen flow rate. NO profiles between 25 and 40 km were obtained during a period of slow descent in the late morning of September 17, 1987 and in the early afternoon of June 18, 1988. The two NO profiles obtained between 35 and 40 km differ by less than 10%. The average NO concentration was 9 ppbv at 35 km, the NO concentration in September was 20 to 35% larger than taht in June. The difference in the temperature profile significantly contributes to the observed change in the NO concentration through the change in the [NO>/[NOx> ratio. These measurements provide an accurate determination of the daytime mid-latitude NO concentration in the upper stratosphere in summer and autumn. ¿ American Geophysical Union 1989