Direct measurements of the nitric oxide concentration between 42 km and 60 km have been made with a rocket-borne chemiluminescent detector. The first flight of this instrument was primarily a demonstration of feasibility; some instrument parameters were not measured but, instead, calculated assuming a standard atmosphere (USSA 1962) and a known vehicle velocity profile. The rocket was fired from Wallops Island, Virginia on 8 April, 1975 at 1405 LT.