Visually responsive neurones of the cat's suprageniculate nucleus were categorized according to their responses to a variety of different types of light stimuli. Their velocity preferences were assessed quantitatively and have been found to predominate in the high range. The positions and dimensions of their receptive fields were determined and these tended to be found within a zone between the vertical meridian and 30-35 degrees. Receptive fields had mean diameters smaller than those reported by others for the pulvinar-LP complex. From these and other electrophysiological data, inferences have been made of the likely sources of afferents providing visual driving. A proposal is offered for SGn visuotopic organization based on correlations of receptive field location with cell position, as determined through electrode track reconstructions.