A new immunoassay (ELISA) based on an antiserum that preferentially recognizes the free form of the pyridinoline (Pyr) crosslink was used to assess the urinary excretion of Pyr in a large normal sample of the population comprising 236 men and 193 women 30-90 years of age. Urinary Pyr increased significantly with age in both sexes. In women Pyr was higher than in men (57 +/- 21 versus 46 +/- 17 nmol/mmol creatinine, p < 0. 001), and the menopause was reflected by a mean 37% increase, from an average 43 to 59 nmol/mm creatinine (p < 0. 001). In 52 patients with active Paget's disease of bone, Pyr excretion was markedly increased (206 +/- 160 nmol/mmol creatinine, p < 0. 001 versus controls) and decreased by 71% after 3 days of IV treatment with the bisphosphonate pamidronate VSports手机版. Free Pyr measured by the ELISA and the total urinary excretion measured by HPLC were highly correlated both in normals (n = 74, r = 0. 83, p < 0. 001) and in Pagetic patients (n = 20, r = 0. 93, p < 0. 001). The mean intra- and interassay coefficients of variation of the ELISA were below 9 and 15%, respectively. It is concluded that this new convenient immunoassay of Pyr should be valuable for the clinical investigation of patients with osteoporosis and other metabolic bone diseases. .