Critical flicker fusion was determined over a wide luminance range for six Siamese and four normal cats. The Siamese cats had the lowest CFF at all luminance levels when compared to normal and binocularly deprived (BD) cats. The Siamese cat's inferior temporal resolution is most likely due to their profound y-cell loss because (1) CFF is proportional to y-cell population across normal, BD, and Siamese cats; and (2) unlike BD cats, the visual cortex of Siamese cats is comparatively normal. The implication of this finding for the CFF of dark-reared cats and normal cats viewing a stimulus which does not stimulate y-cell is discussed.