We performed a comparative study on the sensitivity of the determination of several biochemical markers of bone resorption: urinary calcium/creatinine, free pyridinolines (F-Pyr), free deoxypyridinoline (F-Dpyr), carboxyterminal telopeptide of collagen I (CTX) and aminoterminal crosslinked telopeptides of collagen I (NTX) in the study of postmenopausal osteoporosis. The study included 19 untreated osteoporotic postmenopausal women, aged 59 +/- 6 years, range 46-70 and 16 healthy control postmenopausal women, aged 56 +/- 7 years, range 48-70 years. The following bone markers were determined in 2-h fasting urine samples: calcium/creatinine (atomic absorptiometry), F-Pyr (ELISA, Metra), F-Dpyr (ELISA, Metra), CTX (Crosslaps, Cis bio International) and NTX (ELISA, Osteomark, OSTEX). Values of all markers were expressed as urinary creatinine (Cr) ratios. We found a significant increase in all the studied biochemical markers of bone resorption in osteoporotic patients with respect to control women. Areas under receiver operating characteristic (ROC) curves corresponding to F-Pyr/Cr, Calcium/ Cr, NTX/Cr, CTX/Cr and F-Dpyr/Cr were 74%, 75%, 93.4%, 95.7% and 96% respectively. There were no significant differences among the areas of the ROC curves corresponding to NTX, CTX and F-Dpyr, but areas under urinary calcium and F-Pyr were significantly lower. Among the biochemical markers of bone resorption studied, F-Dpyr, CTX and NTX presented the best discrimination between osteoporotic and control women. F-Dpyr/Cr sensitivity was 79% with a specificity of 100%, CTX/Cr sensitivity was also 79% with a specificity of 100% and NTX/Cr sensitivity was 52% with a specificity of 100%.