We report the optic nerve ultrastructural pathology in experimental scrapie and Creutzfeldt-Jakob disease. Vacuoles developed within myelinated axons contained typical secondary vacuoles and curled membranes. These were seen either within the axoplasm or within the myelin sheath which split either at the major dense line or at the intraperiod line. Spongiform changes were accompanied by an exuberant cellular reaction consisting of macrophages and hypertrophic astrocytes. Occasionally, vesicular myelin degeneration and coated vesicles in a close proximity to the myelin were observed.