We have used Sutter's (1987) spatiotemporal m-sequence method to map the receptive fields of neurons in the visual system of the cat. The stimulus consisted of a grid of 16 by 16 square regions, each of which was modulated in time by a pseudorandom binary signal, known as an m-sequence. Several strategies for displaying the m-sequence stimulus are presented. The results of the method are illustrated with two examples. For both geniculate neurons and cortical simple cells, the measurement of first-order response properties with the m-sequence method provided a detailed characterization of classical receptive field structures. First, we measured a spatiotemporal map of both the center and surround of a Y-cell in the lateral geniculate nucleus (LGN). The time-courses of the center responses was biphasic: off at short latencies, on at longer latencies. The surround was also biphasic-- on then off-- but somewhat slower. Second, we mapped the response properties of an area 17 directional simple cell. The response dynamics of the on and off subregions varied considerably; the time to peak ranged over more than a factor of two. This spatiotemporal inseparability is related to the cell's directional selectivity (Reid et al., 1987, 1991; McLean et al., 1989, 1994). The detail with which the time-course of response can be measured at many different positions is one of the strengths of the m-sequence method.