To reassess the clinical utility of serum pyridinoline cross-linked carboxyterminal telopeptide of type I collagen (ICTP), a promising but controversial indicator of bone resorption, we evaluated its performance as a biochemical marker in a 6-month study of a strictly selected population of 76 Japanese postmenopausal and healthy women, 33 recipients of hormone replacement therapy and 43 nonrecipients. We measured bone mineral density (BMD) of the lumbar spine (L2-L4), and serum ICTP, carboxyterminal propeptide of type I procollagen (PICP) and other conventional serum biochemical markers, e.g. bone gla protein (BGP), alkaline phosphatase, calcium and phosphate at the entry and 6 months later. We calculated the percent change between the baseline and 6-month values (delta%) in lumbar BMD and the biochemical markers, individually, and compared the degree of correlations between delta% in BMD and that in the biochemical markers. Delta% in ICTP and delta% in BGP correlated with delta% in BMD negatively and significantly. Especially delta% in ICTP correlated with that in BMD to a high degree (P<0.0001). No significant correlation was observed in other biochemical markers. We concluded that serum ICTP is a sensitive and useful bone resorption marker in the postmenopausal population, which strongly correlates with the change in BMD.