Aim and Background: The aim of the present study was to evaluate correlations between serum osteocalcin, osteoprotegerin and NTX (Cross-linked N-telopeptides of Type I Collagen) and urinary NTX in breast and lung cancer patients with bone metastases. These four markers are considered to have important roles in bone formation, resorption and metastases. Methods: Four markers were determined in the sera of 60 breast cancer and 21 lung cancer patients and healthy controls (n=30). Serum levels were studied using ELISA and EIA. Results: The median levels of serum osteoprotegerin (p<0.001) and osteocalcin (p=0.003) were higher in patients. Significant correlations were observed between the serum NTX-osteocalcin (r=0.431; p<0.001), serum NTX-osteoprotegerin (r=0.42; p=0.003) and serum NTX - urine NTX (r=0.255; p=0.022). Conclusion: We conclude that osteocalcin, osteoprotegerin and NTX are independent diagnostic tools. Due to the ease of urine collection, urine NTX may be applied routinely to allow early detection of bone metastases and indicate progression of the disease.