We have previously identified a 20‐mer peptide of human thyroglobulin (hTg), p2340 (aa2340–2359), which induced experimental autoimmune thyroiditis (EAT) in AKR/J (H‐2^k) and HLA‐DR3 transgenic mice. In this study, we investigated the thyroiditogenic potential of p2340 in ‘high responder’ CBA/J (H‐2^k) and SJL/J (H‐2^s) or ‘low responder’ C57BL/6 (H‐2^b) and BALB/c (H‐2^d) mice. Mice were immunized subcutaneously with 100 nmol of p2340 in complete Freund's adjuvant (CFA) and both the proliferative capacity of their lymph node cells in the presence of p2340 or intact Tg and the production of peptide‐specific antibodies were investigated. The p2340 peptide was found to contain B‐cell and non‐dominant T‐cell epitope(s) in all strains tested. Moreover, it elicited EAT in CBA/J (2/6, infiltration index (I.I.) 1) and SJL/J (5/5, I.I. 1‐3) mice after direct challenge and in BALB/c (4/7, I.I. 1) and C57BL/6 (1/5, I.I. 1) after adoptive transfer of p2340‐primed lymph node cells. P2340 is the first Tg peptide found to be pathogenic in low as well as high responder mouse strains and thus will allow us to investigate mechanisms of EAT induction in a genetically resistant host.