The question of the oxygen distribution in the high atmosphere is examined by studying the departure from photochemical equilibrium. An investigation of the transition region is made, utilizing recent rocket data on atmospheric transmission in the Schumann‐Runge continuum of molecular oxygen. It is concluded that the molecular oxygen distribution above the dissociation region follows the distribution of the main atmosphere and depends on mixing effects. A limit for the time of mixing can be found when times of dissociation, recombination, and diffusion are considered.It is shown that the level of the mesopause is related to the dissociation of the oxygen molecule. Some suggestions are made concerning dynamical effects affecting the airglow, formation of ionospheric regions, and dissociation of nitroge