This paper discusses the constraints on auroral z mode waves implied by damping. Damping of the magnetoinic z mode in a thermal plasma with &ohgr;p ≪Q is calculated and shown to be strong near the gyrofrequency. Analytic formulae for the optical depth of the corresponding absorption layer are presented. Ray tracing calculations are used to investigate the effect of refraction during the propagation of a z mode ray: refraction is found to be particularly important in the vicinity of the gyrofrequency layer and tends to cause the wave vector of the ray to change so that it is strongly damped. The results are applied to models for the generation of auroral z mode waves. A point of particular interest concerns the possibility of explaining observed emissions whose bandwidths straddle the gyrofrequency by an emission mechanism which amplifies waves either only above or only below the gyrofrequency. For a dipolar magnetic field and radial plasma density gradient it is found that a z mode ray in the auroral zone is unlikely to be able to pass through the gyrofrequency layer without significant damping occurring.