Methyl ethyl ketone has been photolyzed at temperatures between 25° and 240 °C., at varying pressures and intensities. Azomethane has also been photolyzed in the presence of methyl ethyl ketone. It is concluded that the ratio of disproportionation to recombination for a methyl and an ethyl radical is of the order of 0.04. The activation energy for the abstraction of hydrogen from the ketone by methyl is 7.4 ± 0.1 kcal., and by ethyl it is 8.0 ± 0.1 kcal.