Late-onset of disturbed vision is a clinical feature of bovine GM1 gangliosidosis. Studies on eight affected calves showed that ocular lesions were confined to the retinae and optic nerves. Myriad tiny white spots were visible by ophthalmic examination of the fundus. These spots were related to protuberances on the vitreal surface caused by distended retinal ganglion cells. The perikaryons of these were packed with dense aggregates of membranous cytoplasmic bodies (MCBs). Similar MCBs were present in the perikaryons of amacrine cells in the inner nuclear layer of the retina. Wallerian degeneration was present in the optic nerves. The lesions were compared with those described in gangliosidosis in man, cats, pigs and dogs. It is suggested that examination of the fundus is a useful clinical procedure in the diagnosis of bovine GM1 gangliosidosis.