In search of new encephalitogenic myelin antigens, the 2′,3′-cyclic nucleotide 3′-phosphodiesterase (CNP) and 19 000 MW isoform of myelin-associated oligodendrocytic basic protein (MOBP) were obtained as recombinant proteins by the baculovirus expression system in Spodoptera frugiperda cells and purified to homogeneity by immobilized metal chelate affinity chromatography (IMAC). The purified MOBP was soluble in water and showed retarded migration on sodium dodecyl sulphate-polyacrylamide gel electrophoresis similar to myelin basic protein (MBP). MOBP induced experimental autoimmune encephalomyelitis (EAE) in nine of 15 susceptible SJL OlaHsd mice, causing death in two animals, whereas three of 14 BALB/c mice showed mild symptoms of EAE, manifested as transient weakness of hind limbs. In both mouse strains, periventricular infiltrates of mononuclear cells were observed. In addition, both 46 000 MW and 48 000 MW CNP isoforms were shown to be non-encephalitogenic for both mouse strains.