Local changes in atmospheric ozone relative to background regional changes over a period during which a small megaton nuclear weapon was detonated in tropical latitudes have been studied by using backscatter UV observations from Nimbus 4 satellite. Little change in total ozone was observed, less than might have been expected from current models of NOx catalytic depletion. A further attempt was made to isolate changes at different levels by using derived ozone profile data from orbits intersecting the envelope containing bomb-modified air without success because of contamination of the data on shorter wavelenghts. We are led to conclude either that NOx yields have been overestimated or that there is an efficient NOx sink in the stratosphere that is not yet recognized.