Over the past decade monoclonal antibodies have been successfully employed in a number of animal models of autoimmune disease. We have used antibodies to the class II gene products of the major histocompatibility complex, the CD4 molecule on helper T cells, and the T-cell receptor. Monoclonal anti-class II antibodies have been administered to treat paralytic disease in the animal model of multiple sclerosis--experimental allergic encephalomyelitis. These antibodies not only reverse acute paralytic disease but also decrease the number of relapses in a model of relapsing/remitting multiple sclerosis when given after the first attack. The advantage of this form of therapy is that it is haplotype specific. In other words, in a heterozygous individual it is possible to block the major histocompatibility gene associated with disease susceptibility while leaving other major histocompatibility gene products free for antigen presentation. Thus, animals given this form of immunotherapy are not significantly immunosuppressed. Antibodies to the CD4 molecule have been equally effective in treating animal models of autoimmunity. We and others have reversed ongoing paralysis in experimental autoimmune encephalomyelitis. Relapses have been diminished after the administration of anti-CD4. Antibodies to CD4 have been used successfully to treat animal models of systemic lupus erythematosus, rheumatoid arthritis and myasthenia gravis. Recent trials with anti-CD4 have been successful in the treatment of rheumatoid arthritis and cutaneous T-cell lymphoma. The latter trial employed a chimeric human/mouse antibody. Antibodies to the variable region of the T-cell receptor have been employed to treat experimental autoimmune encephalomyelitis.(ABSTRACT TRUNCATED AT 250 WORDS)