To further characterize the nature of retinal periphlebitis and retinitis in multiple sclerosis, immunoperoxidase studies were performed on retinal tissue from multiple sclerosis patients at autopsy. Antibodies against myelin basic protein stained the optic nerve but not the retina. Both normal and multiple sclerosis retinas showed staining of Müller cells with Leu-7 (a monoclonal antibody that cross-reacts with myelin associated glycoprotein and natural killer cells). Nerve fiber bundles of the optic nerve in cases with multiple sclerosis and controls also showed staining with Leu-7 antibody. Tissue-bound IgG was demonstrated on retinal ganglion cells in six of seven multiple sclerosis cases but not in controls.