This brief report reviews some of the major studies presenting evidence for altered humoral and cellular immunity in the idiopathic inflammatory myopathies. Clearly, the association of these disorders with other autoimmune diseases, the myriad of myositis-associated autoantibodies, and the phenotypic and functional abnormalities of mononuclear cells from PM/DM patients, all suggest that autoimmune mechanisms are central and pervasive aspects of these diseases. Yet, the current experimental limitations in immunology, as well as the rarity and heterogeneity of the idiopathic inflammatory myopathies, combine to limit our understanding of which factors are primary, and which are only secondary epiphenomena, in the complex pathogenesis of these disorders.