Chronic debilitating diseases such as multiple sclerosis, demyelinating inflammatory polyradiculoneuropathy, rheumatoid arthritis, diabetes mellitus type I, Hashimoto thyroiditis, forms of uveitis and interstitial nephritis, share many characteristics. They are all organ-specific inflammatory diseases of unknown etiology but with strong evidence of tissue-destructive activity of the cellular immune system in the organs respectively affected, i.e. the central or peripheral nervous system, the joints, the islets of Langerhans, the thyroid gland, the retina, or the tubulo-interstitial renal tissue. Recognized animal models of all these diseases are experimentally induced autoimmune conditions that are transferable with autoreactive T-lymphocytes, in contrast to autoantibodies in humoral autoimmune diseases. In recent years, disease-transferring T-lymphocytes, have been successfully grown as lines and clones in vitro, thus finally proving the primary pathogenic role of autoreactive T-lymphocytes in these animal models. Such T-cell lines are valuable tools in further defining autoantigens, studying mechanisms of T-cell activation in vitro, following T-cell migration and organ-specific homing in vivo, and analyzing effector functions in the infiltrated organs. In addition, questions concerning the breakdown of immunological selftolerance and the basic principles of resistance to disease can be addressed, and possibilities of treatment can be approached. Although the basic etiology of the human organ-specific immune diseases is still unknown, these animal models have helped to throw light on some of the pathogenic mechanisms common to these various diseases.