The responses of receptive fields of the cat lateral geniculate body to stimuli of different contrast were investigated. The neuronal responses increased linearly with the stimulus contrast when the contrast change with variation in the test stimulus intensity. This relation was nonlinear when background intensity was changed. The calculation of the number of impulses in different time intervals of the response (deltat) indicated that the dependence of this number on the contrast is the steeper, the larger deltat during the first 70-90 ms of the response. The Weber-Fechner law holds for the lateral geniculate body receptive fields.