E-Mail Bone turnover markers (BTMs) in blood and urine are useful tools in monitoring osteoporosis treatment effects and may be useful for improving patient adherence. In 2011, a Joint Committee on Bone Metabolism of the International Osteoporosis Foundation (IOF) and the International Federation of Clinical Chemistry and Laboratory Medicine (IFCC) designated Procollagen type I N-propeptide (PINP) and the C-terminal telopeptide of type I collagen (β-CTX) in blood as reference bone turnover markers for bone formation and bone resorption, respectively, in osteoporosis. However, the effective clinical implementation of these recommendations requires the standardization/harmonization of commercial assays [1]. As well as a review of the structures of PINP and β-CTX molecules, the authors provide a succinct, referenced summary of current commercial assays, their descriptions, and performance characteristics. Key characteristics and performance specifications of the four commercially available assays for serum PINP and the three commercially available β-CTX assays are provided, as well as regression equations for the Roche and IDS iSYS automated assays for PINP and β-CTX.