Type 1 diabetes is thought to be an autoimmune disease mediated by T lymphocytes recognizing critical islet cell antigens. Recently, the tyrosine phosphatase like protein IA-2 was suggested as a putative autoantigen in type 1 diabetes since autoantibodies are detected in sera of diabetic patients and prediabetic subjects. Similarly, T cell responses of peripheral blood lymphocytes of type 1 diabetic patients to this protein have been described. Only very few data is available about immunodominant epitopes of IA-2 recognized by T cells. We have studied T cell responses in type 1 diabetic patients and age and partly HLA matched controls to IA-2 peptides designed to bind HLA risk alleles of IDDM as DR* 0401 and DQ* 0302. Both diabetic patients and controls responded to IA-2ic and some of the peptides. Three peptides of the C-ter-minal region of IA-2 were recognised by T cells of a fraction of diabetic patients but at least two of these peptides triggered also T cell responses in DR* 0401/DQ* 0302-matched controls. Most pep-tides bound to different HLA alleles (“promiscous binders”). The identification of autoantigenic epitopes may offer clues to related sequences eg of viral origin what relates to models of diabetes pathogenesis (“molecular mimicry”). Secondly, the design of antigen-or even epitope-specific immune intervention strategies aiming at tolerization of disease specific T cells in type 1 diabetes may profit from the knowledge of immunodominant T cell epitopes of a putative autoantigen.