Pyridinoline and deoxypyridinoline are intermolecular cross-links in mature collagen in bone and cartilage. The urinary excretion of the two compounds correlates well to bone turnover. A fast, sensitive, and accurate isocratic ion-pairing reverse-phase high-performance liquid chromatography method for measurement of pyridinoline and deoxypyridinoline in urine has been established. Intra- and inter-assay precision were 5-7% and 12-14%, respectively. Recovery for pyridinoline was 97.4% and for deoxypyridinoline 94.3%. The detection limit was 0.4 pmol. Pyridinoline:creatinine and deoxypyridinoline: creatinine ratios in healthy subjects, were 38.8 nmol:mmol and 13.0 nmol:mmol, respectively. Increased values of both cross-links were observed in children, in the age group 20-29 in both sexes, and in post-menopausal women.