A summary is presented of the relative importance of the principal aeronomic processes determining the vertical distribution of NO-NO2 in the stratosphere. Formation and destruction of nitric oxide are considered with transport processes for steady-state conditions. Estimates of the vertical distribution of NOx are made for extreme conditions of the eddy diffusion coefficient. It is pointed out that NO is determined by the values which are adopted for its photodissociation coefficient which is related to the absorption of solar radiation in the Schumann-Runge bands of molecular oxygen.