Auroral hiss is attributed to amplified Cerenkov emission of nearly resonant whistlers. such emission occurs only when the pricipitating electron flux corresponds to a one-dimensional distribution with a peak in parallel energy. Only particles below this peak contribute to the amplified emission. The back reaction of the hiss on the electrons is treated by using quasi-linear theory. The primary effect is to reduce the positive gradient in energy below the peak. This tends to suppress the generation of the waves. A relation between the expected intensity of the hiss and the properties of the stream is derived. The observational data are consistent with limitation of the intensity by quasi-linear relation.