Eyes of cutaneous melanoma-bearing miniature Sinclair swine were examined by light and electron microscopy during growth and maturation of animals. The histology of ocular depigmentation, which occurs during melanoma arrest and skin depigmentation, was studied in eyes of animals that had successful and unsuccessful tumor regression. In 12 animals one eye was removed at an early stage and the second eye at a later stage of disease or maturation. The histologic and clinical course of the ocular changes was correlated with changes in the cutaneous tumors. Animals showing rapid cutaneous tumor regression developed acute uveitis that was characterized by an influx of mononuclear cells into the stroma of the ciliary body; later this spread to the iris and choroid. In late stages the cornea sometimes developed a band of calcium precipitates beneath the basal epithelial cells (band keratopathy). Uveal melanocytes developed watery cytoplasm typical of cells with ruptured plasma membranes. Released melanin granules were taken up initially into the lysosomal compartment of mononuclear cells having the various morphologic features of lymphocytes and monocytes; later, melanin also appeared in fibrocyte lysosomes. The relationship of these processes to various cell-mediated immunity phenomena is being studied.