Corticothalamic neurons in area 17 of the cat were identified by electrical stimulation of the dorsal lateral geniculate nucleus. Histological reconstruction showed most of the cells to be in lamina VI. The majority (23 out of 30) of corticothalamic cells were classified as simple, the remaining units had complex receptive fields. Simple cells had more slowly conducting axons than complex cells and it is suggested that there are two subgroups within the population of corticothalamic neurons. The implications of the simple cell projection are discussed both in relation to the possible role of the corticothalamic feedback and to the organization of processing within the striate cortex.