Bactobolin, a novel antineoplastic and antibiotic, was tested for prevention and treatment of experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Clinical and histological signs of EAE induced by active challenge with myelin basic protein and Freund's complete adjuvant were profoundly suppressed by prophylactic treatment with bactobolin during the inductive phase of EAE in association with diminished lymphocyte proliferative response to sensitized antigens. It was also effective on the effector phase of actively induced EAE as well as passively induced EAE with primary cultured spleen cells sensitized to myelin basic protein. Moreover, therapeutic administration of bactobolin after onset of EAE was effective. The results suggest possible usefulness of bactobolin for treatment of autoimmune disease.