A determination of the NO2 and O3 mixing ratios has been made by measuring the attenuation of sunlight at 409 nm and 254, 288, 316 nm from an ascending rocket launched from Kourou, French Guiana (5 ¿N) during the morning twilight of March 21, 1974. A peak NO2 volume mixing ratio of 4.4¿10-9 +40-50% was measured at 30 km altitude.