Insulin‐dependent (type 1) diabetes is characterized by progressive destruction of insulin‐producing β cells probably by autoreactive T lymphocytes. Viral infections, especially those caused by coxsackieviruses, are postulated to play a role in the pathogenesis of the disease in humans. One mechanism by which viral infections could initiate or accelerate diabetogenic processes is “molecular mimicry,” induction of antiviral immune responses cross‐reacting with epitopes in the β‐cell autoantigens. Tyrosine phosphatases (IA‐2, IAR) represent a major target autoantigen in type 1 diabetes. Both humoral and cellular immune responses are directed to the carboxy‐terminal (C‐terminal) part of the protein. This region has a 5‐amino acid sequence identity, followed by five amino acid similarity with the conservative motif in the VP1‐protein of enteroviruses (PALTAVETGA/HT), which is a highly immunogenic B‐ and T‐cell epitope in enterovirus infection‐induced immune responses. This observation prompted us to investigate potential humoral cross‐reactions between immune responses induced by tyrosine phosphatases and enteroviruses. The reactivities of various peptide‐ and virus‐induced rabbit antisera clearly demonstrated that cross‐reactions do exist, and in both directions. Using epitope mapping, we were able to show that several diabetes‐linked epitopes in IA‐2 were also recognized by CBV‐4‐induced antisera. Immunization of female NOD‐mice with formalin‐inactivated purified strain of coxsackievirus B4 (CBV‐4‐E2) induced an immune response that recognized the IA‐2/IAR diabetogenic peptide. The results obtained with human paired sera, collected during enterovirus infection, indicated that enterovirus infection in humans may also occasionally induce a humoral response that cross‐reacts with IA‐2/IAR. J. Med. Virol. 66:340‐350, 2002. © 2002 Wiley‐Liss, Inc.