IL-17–producing T cells are regarded as potential pathogenic T cells in the induction of autoimmune diseases. Previously, we have shown that injection of adjuvants containing Mycobacterium, such as CFA or bacillus Calmette-Guérin, can prevent type 1 diabetes in NOD mice. We injected NOD mice with mycobacterial products sc and analyzed the IL-17–producing cells from the draining lymph nodes and spleen by restimulating whole-cell populations or CD4+ T cells in vitro with or without IL-17–polarizing cytokines. Mice receiving CFA had a concomitant rise in the level of IL-17, IL-22, IL-10, and IFN-γ in the draining lymph node and spleen. Adoptive transfer of splenocytes from CFA-injected NOD mice polarized with TGF-β plus IL-6 or IL-23 delayed the development of diabetes in recipient mice. IL-17–producing cells induced by CFA maintained their IL-17–producing ability in the recipient mice. Injection of CFA also changed the cytokine profile of cells in pancreatic tissue by increasing IL-17, IL-10, and IFN-γ cytokine gene expression. We suggest that the rise in the level of IL-17 after adjuvant therapy in NOD mice has a protective effect on type 1 diabetes development.