Mixing ratios of nitric oxide were measured by the chemiluminescence method as part of the 1977 and 1978 Global Atmospheric Measurement Experiment of Tropospheric Aerosols and Gases (Gametag) missions. Since the method is not highly specific it can provide only upper limits for the NO mixing ratio. Values for maritime air were ?30--40 parts per trillion by volume (pptv) and showed little variation with latitude or whether or not the measurements were taken in or above the boundary layer. Over continental North America mixing ratios in unpolluted air were ?40--60 pptv, independent of altitude. Values in excess of 1 ppbv were obtained in industrial regions, over forest fires, and even over small Eskimo villages in northern Canada. In polluted air the values decreased with an increase in altitude.