D-penicillamine holds the key to a better understanding of autoimmunization and the pathogenesis of autoimmune disease. Analysis of its mode of action is complicated by its multiplicity of effects. In respect to anti-acetylcholine receptors and myasthenia gravis, the major effect may be at the level of immunoregulation and/or immunogenicity. Anti-striated muscle antibody is much more common and is influenced by the HLA antigen of the patient. Thus, HLA-linked immune response genes may be involved.