The biosynthesis of collagen involves a number of unique post-translational modifications which are catalyzed by many specific enzymes. The main steps in collagen biosynthesis are transcription and translation, hydroxylations of prolyl and lysyl residues, glycosylations of hydroxylysyl residues, chain association and disulphide bonding, triple helix formation, secretion of procollagen into the extracellular matrix, conversion of procollagen into collagen, specific aggregation of collagen molecules and crosslink formation. Information about these modifications has rapidly increased during recent years, and initial information is available about the regulation and possibilities of specific pharmacological control of collagen biosynthesis at the level of these stages. Elucidation of the biochemical defect in an inborn error of collagen biosynthesis in man was reported for the first time in 1972 and subsequently several additional defects have been characterized. Alterations in collagen biosynthesis are also found during growth and ageing, as well as in many acquired pathological states: data about the nature of such changes in now rapidly accumulating.