Type 1 collagen is the major collagen in the body and is mainly found in mineralised bone. It has a triple helical structure consisting of one α1 and two α2 chains which are linked by disulphide bonds. The molecule is synthesised as procollagen which is proteolytically cleaved to remove both the N‐ and C- terminal parts of the molecule prior to the assembly of the remainder into the collagen matrix. The N‐ and C‐terminals are released into the circulation stoichiometrically and thus reflect the synthesis of new type 1 collagen.The amino-terminal propeptide of type I procollagen (PINP) is probably the most specific and sensitive marker of bone formation. PINP is a useful marker for monitoring the efficacy of osteoporosis therapy with anabolic agents, but it is also one of the best bone turnover markers for monitoring the efficacy of anti-resorptive therapy.