Hydroxyproline (4-hydroxyproline) is a common nonproteinogenic amino acid. It is found only in collagen and elastin in mammals but exists in a number of other proteins in plants. Hydroxyproline is formed only as a post-translational modification in the peptide chain and proline hydroxylase does not hydroxylate free proline. Hydroxyproline in tissue hydrolysates is a direct measure of the amount of collagen or gelatin present. A variety of disease states are believed to affect collagen turnover and can cause elevated serum or urine hydroxyproline. Such conditions range from neoplastic, inflammatory, renal or bone disease to endocrine and autoimmune disorders. Hydroxyproline Assay Kit is designed to measure hydroxyproline in tissue or protein/peptide hydrolysates. It can be used to measure hydroxyproline from other biological samples such as serum or urine if they have undergone a prior purification process. It is an easy, convenient method which results in a chromogen with an absorbance maximum at 560 nm. The assay is useful over the range of 0.1-2 μg.