During the NASA GTE/CITE 1 fall 1983 airborne field operation the NASA Convair 990 penetrated the anvils of two active cumulonimbus clouds. While NO levels outside the anvils averaged about 20 parts per trillion per volume (pptv), the average NO inside the anvils was about 440 pptv. Extrapolation of this observation along with data on the amount of air typically advected out of cumulonimbus clouds and the total number of thunderclouds occurring over the globe at any moment, implies a rate of nitrogen fixation in electrified clouds of about 7¿106 t/yr. Although the data base used to make this estimate is quite limited, our approach differs from that used in previous studies of the global production of nitrogen oxides by lightning and thus represents an independent assessment of the role of electrified clouds in the atmospheric nitrogen oxide budget. ¿American Geophysical Union 1987