The non-Gaussian response of a simple polynomial non-linear element to Gaussian excitation is investigated, and correlation functions and spectral densities up to the fourth order are established in terms of the second order correlation function and spectral density of the excitation. Suitable choice of excitation and non-linearity parameters then permits the response to be used, either in analysis as a well-described near-Gaussian random process, or as a good approximate model of any given near-Gaussian random process.