The pyrolysis of acetaldehyde oxime in the presence of nitric oxide has been studied between 240 and 280 °C. The pyrolysis of nitrosoethane alone and with nitric oxide has been studied between room temperature and 120 °C. The results are shown to accord with the mechanisms predicted for these pyrolyses. They agree in essence with those proposed for the high-temperature pyrolyses of ethane and n-butane in the presence of nitric oxide, in which the oxime and nitroso-compounds are involved as unstable intermediates, although the lower temperature reactions are complicated by heterogeneous processes.