Collagen type I is present in soft connective tissue and bone where it represents approximately 90% of the organic matrix. Collagen type I is produced from procollagen when two teloterminal propeptides are digested from the procursor and released into the circulation. The propeptide levels can be measured in serum as indicators of collagen production. Elevated values of these propeptides in serum are found in patients with various bone metabolism defects. Procollagen type I C-terminal propeptide (PICP) has a molecular weight of approximately 100kD and the normal range in serum is 100-300ug/ml.