Ethyl Michlers ketone oxime EMKO is a reagent that has been useful as a detector of phosphorylating and phosphonylating agents, but its susceptibility to degradation has limited its serviceability. In an effort to overcome this difficulty, it has become necessary to consider the oxidative and photochemical degradation of EMKO. A study of the oxidation of EMKO was started on the hypothesis that free radicals, which are important intermediates in the course of many oxidations, are formed in the early stages of EMKO degradation in air or light or both. Attempts to detect free radicals by means of electron-spin resonance spectroscopy were made and the isolation and identification of oxidation products was attempted. Free radicals were not detected, but several oxidation products were isolated and identified. Subsequently, the photochemical degradation of EMKO on thin-layer supports was studied and several products isolated and identified. Differential thermal analysis DTA studies were conducted at the same time. The treatment of EMKO with metal-type oxidizing agents leads predominantly to Beckmann rearrangement products rather than to oxidation products. This unexpected course of action perhaps explains why free- radical products of EMKO were not detected. The photochemical degradation of EMKO leads to several products among which are EMKO, the anilide, the nor-ethyl anilide, and ethyl Michlers ketimine. The presence of these compounds was rationalized in several ways and these mechanisms were tested. The kinetics of the photoreaction in solution are complicated and no consistent interpretation is available at this time.