FK506 binding protein 12.6 kDa (FKBP12. 6), a protein that regulates ryanodine Ca 2+ release channels, may act as an important regulator of insulin secretion. In this study, the role of FKBP12. 6 in the control of insulin secretion and blood glucose is clarified using FKBP12. 6−/− mice. FKBP12. 6−/− mice showed significant fed hyperinsulinemia but exhibited normoglycemia, fasting normoinsulinemia, and normal body weight compared with wild-type (WT) littermate control mice. Deletion of FKBP12. 6 resulted in enhanced glucose-stimulated insulin secretion (GSIS) both in vivo and in vitro, a result that is due to enhanced glucose-induced islet Ca 2+ elevation. After a high-fat dietary challenge (HF diet) for 3 mo, FKBP12. 6−/− mice displayed higher body weight, hyperinsulinemia, and lower fed blood glucose concentrations compared with WT mice. FKBP12. 6−/− mice displayed hyperinsulinemia, and resistance to HF diet-induced hyperglycemia, suggesting that FKBP12. 6 plays an important role in insulin secretion and blood glucose control, and raising the possibility that it may be a potential therapeutic target for the treatment of type 2 diabetes.—Chen, Z., Li, Z., Wei, B., Yin, W., Xu, T., Kotlikoff, MI, Ji, G. FKBP12. 6-knockout mice display hyperinsulinemia and resistance to high-fat diet-induced hyperglycemia.