The ocular pathology of mannosidosis was studied In the bovine model. There was widespread vacuolation of many cell types including corneal epithelium, Bescemet's endothelium, corneal fibroblasts, pigraented cells, lens epithelium, lens fibres, pigment epithelium and all cell types of the neuroretina. On electron-microscopy most vacuoles were seen to be membrane bound vesicles compatible with being secondary lysosomes and similar to those previously described elsewhere in the body. Additional vacuoles were seen due to dilatations between lens epithelial cells and between lens fibres. The cause of lens and corneal opacities seen in human patients is unclear from the present study but are presumably a consequence of the lesions noted.