NTx and I CTP, a metabolite of type I collagen, were compared as to their usefulness as indicators of bone metastasis in lung cancer. The NTx level was significantly higher in lung cancer patients with bone metastasis (107.9 +/- 56.1 nM BCE/mM) than in those without it (p < 0.0001), as was the I CTP level (10.0 +/- 6.5 ng/ml; p < 0.0001). The Z scores of NTx and I CTP were 2.37 and 2.04, respectively, indicating that NTx is superior to I CTP in sensitivity to bone metastasis because of its higher Z score and its higher area under the ROC curve. The cutoff values of these markers were set to produce the highest accuracy/sensitivity rates and to make possible the highest diagnostic efficiency, and then the odds ratios at these cutoff values were calculated. The odds ratios of NTx and I CTP at cutoff values for the highest accuracy were 66.3 and 12.6, respectively; those offering the highest diagnostic efficiency were 46.5 and 10.0, respectively. These results indicated that NTx offers better prediction of bone metastasis in lung cancer than does I CTP.