Type 1 diabetes is under polygenic control both in humans and the NOD mouse. Recently a possible role of IL-21 in the pathogenesis of type 1 diabetes was demonstrated in the NOD mouse. Furthermore, the murine IL-21 gene is mapped to the Idd3 interval, making the human IL-21 gene (IL21) a functional as well as positional candidate for susceptibility. We therefore screened sequence variants of IL21 and studied the association with type 1 diabetes. Preliminary data showed no association of IL21 polymorphisms with the disease, suggesting that IL21 plays little role in susceptibility to type 1 diabetes in Japanese.