The number of ganglion cells in the cat's retina, and the pattern of their distribution over the retina, have been reinvestigated. Criteria are presented for the identification of ganglion cells in Nissl-stained whole mounts, most particularly for the distinction between small ganglion cells and neuroglial cells, by reference to retinas with no ganglion cells (obtained by nerve section) and to areas to retina containing a population of only small ganglion cells (obtained by optic tract section). Using these criteria, the number of ganglion cells was counted in four retinas (mean total 116,250). The number of large or "giant" cells (presumably the somas of Y-cells and of alpha-cells) varied from 4,200 to 7,100. Overall these cells comprised 4.0-6.3% of the total ganglion cell population. Their distribution over the retina showed a concentration around the area centralis, with a localized minimum density at the area centralis, and a concentration in the visual streak. These concentrations of large cells were quantitatively less than the concentrations of smaller cells in the area centralis and visual streak, so that the relative frequency of large cells was minimal (mean 1.6%) at the area centralis and increased steadily up to 5.5-6.9% in peripheral retina. Their relative frequency was distinctly lower along the visual streak than in peripheral retina above or below the streak.