Firing rates of ganglion cells were measured by extra cellular recording in cat retina. in response to sinusoidally modulated light intensity applied full-field. Upon averaging at least 10 cycles of response, the firing rate variation was found to be approximately sinusoidal at an average value. Response parameters phase, magnitude and average value were correlated with stimulus parameters magnitude and frequency. Differences in transfer characteristic among on, off, and on-off responding cells are shown. Phase of response relative to stimulus in concluded to be a good measure of cell response type. That all types of retinal ganglion cells are involved in the transmission of information about light increases and decreases is implied by the evidence that retinal dark discharge functions as a carrier, which is modulated at least by light intensity. No linear mathematical model can account for all the data presented.