28 consecutive patients with multiple osteolytic bone metastases due to various types of cancer were treated with 300 mg/day of sodium clodronate given intravenously as a 3-hour infusion. 16 patients were treated for 10 days and 12 for 20 days. Our findings showed that clodronate administration causes an increase in serum osteocalcin (sBGP) in the group of patients treated for 20 days (p < 0.05), a reduction in serum Ca in both groups of patients (p < 0.01), an increases in serum alkaline phosphatase (p < 0.05 and p < 0.01), a reduction in urinary Ca (p < 0.01) and a reduction in uOHP (p < 0.05). The raise in sBGP may be attributed to the reduction of sCa and to the consequent secondary hyperparathyroidism. The increase in sBGP can be considered as the expression of osteoblasts stimulation following an adequate period of therapy with sodium clodronate.