A comparison has been made of five methods for terminating the reaction of active nitrogen with ethylene in the temperature range 295° to 673° K. These were based on deactivating the active nitrogen by low-temperature trapping, by addition of nitric oxide, and by passing it over copper oxide or cobalt catalysts. With the nitric oxide and cobalt catalyst techniques, which appeared to be the most reliable of those used, an activation energy of 400 ± 200 cal/mole, with a P factor of about 10−5, have been determined for the reaction.