Extracellular single-unit recordings were undertaken in the retina of the rhesus monkey in order to assess the receptive-field properties of those ganglion cells which project to the superior colliculus. Cells were tested for antidromic activation from the superior colliculus, lateral geniculate nucleus, and the optic chiasm. 2. The majority of retinal ganglion cells could be classified as color opponent or broad band. A small, heterogeneous group could not be so classified and were collectively referred to as "rarely encountered" cells. 3. Color-opponent cells responded in a sustained fashion and broad-band cells in a transient fashion to visual stimuli. Quantitative assessment of response transiency shows that this measure reliably differentiates these two classes. 4. To moving sinusoidal gratings broad-band cells responded more vigorously and with greater temporal modulation than did color-opponent cells. 5. The distributions of conduction velocities of different classes of neurons showed considerable overlap. On the average, axons of broadband neurons conducted most rapidly and rarely encountered types, most slowly. 6. The population of cells projecting to the superior colliculus does not contain color-opponent cells. The retinotectal cells respond predominantly in a transient fashion. Only 3.9% of broad-band cells (26 of 663) were antidromically driven from the superior colliculus, while 29% of the rarely encountered group (5 of 17) could be so activated. 7. The relative distribution of color-opponent and broad-band cells does not appear to change with retinal eccentricity within the central 20 degrees.
