Myelin oligodendrocyte glycoprotein (MOG) is a transmembrane protein belonging to the immunoglobulin superfamily and contains an Ig-like domain followed by two potential membrane-spanning regions. MOG is expressed only in the CNS with very low content (approximately 0.1% total proteins) in the oligodendrogliocyte membrane. Three possible functions for MOG were suggested: (a) a cellular adhesive molecule, (b) a regulator of oligodendrocyte microtubule stability, and (c) a mediator of interactions between myelin and the immune system, in particular, the complement cascade. A direct interaction might exist between the membrane-associated regions of MOG and the myelin-specific glycolipid galactocerebroside (Gal-C), and such an interaction may have important consequences regarding the membrane topology and function of both molecules. It is considered that MOG is an autoantigen capable to produce demyelinating multiple sclerosis-like diseases in experimental animals.