By means of immunoreactivity for spot 35 protein, a novel cerebellar Purkinje cell-specific protein, the regional heterogeneity among non-pigmented ciliary epithelial cells of rats was demonstrated with reference to the antero-posterior and crest-valley directions of individual ciliary epithelial folds in immature and mature eyes. The functional significance of the occurrence of the spot 35 immunoreactivity in the posterior portion of the ciliary epithelium is briefly discussed in relation to the formation of the aqueous humor.