While immunosuppressive drugs now permit good control of acute allograft rejection, chronic rejection remains an important medical problem, and the induction of stable transplantation tolerance has not yet been achieved in patients. 1,25-Dihydroxyvitamin D3 (1,25(OH)2D3), a secosteroid hormone that controls cell proliferation and differentiation and exerts immunoregulatory activities in addition to regulating calcium and bone metabolism, has the potential to contribute to the management of allograft rejection. Recent advances in understanding the immunomodulatory properties of 1,25(OH)2D3 and its analogs suggest the clinical application of these hormones in transplantation, with the aim of facilitating tolerance induction and preventing chronic graft rejection.