Parathyroid hormone(PTH) is essential for maintaining serum calcium level. PTH increases serum calcium partly by enhancing bone resorption. Therefore, persistent excessive actions of PTH result in cortical bone loss by increased bone resorption. In contrast, intermittent injections of PTH preparations increase trabecular bone mainly by enhancing bone formation. Teriparatide is a peptide with 34 amino acids corresponding to the N-terminal portion of PTH. Both once daily and once weekly subcutaneous injections of teriparatide are available in Japan. Teriparatide was shown to prevent vertebral fractures. In addition, once daily injections of teriparatide also reduce non-vertebral fractures. However, there still remain several unanswered questions about the precise mechanisms of actions of teriparatide preparations.