A high performance measurement system based upon NO/O3 chemiluminescence has been developed for simultaneous measurements of the title species using smaller aircraft such as the NCAR Sabreliner. NO is determined directly, NO2 is converted to NO by broad-band photolysis, NO(y) is converted to NO using gold-catalyzed reduction in the presence of CO, and O3 is determined using excess NO as the reagent. The system is capable of measurements of the odd nitrogen species at levels below 10 pptv. A description of the instrument and its application to some flights within a thunderstorm are presented.