The relationships between luminance and height, width or area of the feline pupil were investigated in awake, normal adult cats whose pupils were photographed over a range of light levels with the aid of electronic flash. The results are compared with previous measurements of pupil width and height in awake animals (Kappauf 1943); and with estimates of pupil width, height and area in lightly-anaesthetised cats (Wilcox and Barlow 1975). The implications of these results for retinal illumination and colour discrimination are discussed.