Type I collagen is synthesized by the osteoblasts, and accounts for more than 90% of the organic matrix of bone. A new specific immunoassay was used for assessment of serum carboxy-terminal telopeptide of type I collagen, (ICTP), which is one of type I collagen degradation products. ICTP proved to be specific non-invasive marker for bone resorption. Also it can be used in early detection of bone metastasis before being diagnosed by bone scan. ICTP was measured in both metastatic as well as non-metastatic groups of patients of lung cancer with bone metastasis. It was found that at a cut-off value of 5.5 μg/ L its diagnostic sensitivity was 96.2 %, specificity was 86.6 % and diagnostic accuracy was 92.8 %.