Bone metastases are common in breast cancer. Bone metastases are difficult to evaluate clinically. To establish the significance of measurement of osteoblastic and osteoclastic activity in serum as an indicator for bone metastases in breast cancer, biochemical markers of bone turnover were estimated in patients with breast cancer. Fifty breast cancer patients were included in this study; 25 patients without bone metastases and another 25 patients with bone metastases according to their last bone scan. 30 healthy controls were also included. Biochemical markers of bone formation: total alkaline phosphatase and it's bone isoenzyme (by gel electrophoresis), osteocalcin, and PICP by RIA and bone resorption markers: total acid phosphatase and tartarate resistant acid phosphatase serum and urinary calcium as well as CA15-3 were performed in all groups. Comparative study revealed a highly significant increase in total alkaline phosphatase, it's bone isoenzyme activity and osteocalcin in group II (bone metastatic breast cancer group). The results also revealed a highly significant increment in total acid phosphatase, tartarate resistant acid phosphatase, urinary calcium/creatinine, and serum calcium in group II. A highly significant increment in PICP and CA 15-3 were found in group I and II. A positive correlation was found between bone isoenzyme alkaline phosphatase and tartarate resistant acid phosphatase in group II. No significant correlation between bone isoenzyme alkaline phosphatase and markers of bone formation and bone resorption in group I (non bone metastatic breast cancer group). In conclusion bone isoenzyme alkaline phosphatase and tartarate resistant acid phosphatase can be considered markers of bone metastases in breast cancer patients.