Soil emissions of NO and NO2 were measured at forest and agricultural sites in Pennsylvania. The strong dependence of NO emissions on soil temperature observed in earlier studies was also found in these measurements. The large variation in the measured NO flux at these sites indicated that variables other than soil temperature play an important role. In the present study the strong correlation between the NO flux and the soil nitrate level suggests that the level of available nitrate in the soils may affect NO emission. In this connection it should be noted that the application of chemical pesticides, as well as nitrate-containing fertilizer, may influence these results. In these studies, NO2 accounted for a minor fraction (6%) of the nitrogen oxide emissions. Laboratory studies designed to investigate the influence of certain environmental factors on NO emissions under controlled conditions were also conducted. These results also indicate that temperature has a large effect on soil NO emissions, while flush gas humidity and carbon dioxide level exert little, if any, effect. ¿ American Geophysical Union 1988