The electroretinogram (ERG) response to steadily flickering fields shows significant nonlinear components. These nonlinear components have been used to investigate the ERG. We find the following. (1) The fundamental retinal response can be recorded at frequencies greater than 100 Hz and the second and higher harmonic responses have measurable response frequencies as high as 200 Hz. Both the fundamental response component and the second harmonic response component have multiple local maxima as a function of frequency. (2) Measurement of the response of the retina to the sum of two sine waves indicates that there is an early low-pass temporal filter in the retina. This early filter has a cutoff frequency between 40 and 50 Hz. (3) The high frequency nonlinearity is not a compressive nonlinearity.