The development of histomorphometric and histodynamic investigations has permitted the description of a specific and complex osteopathy in hyperthyroidism. The increased bone turnover rate in hyperthyroid patients may be accompanied by a considerable bone loss. These features are associated with both increased osteoclastic bone resorption and increased osteoblastric bone formation, with an accelerated calcification rate. Conventional biochemical markers of bone metabolism, i.e. serum calcium and alkaline phosphatase and urinary hydroxyproline and calcium are normal in most patients with hyperthyroidism. However, the correlation between serum BGP and serum concentration of thyroid hormon suggests that serum BGP may be a sensitive marker of increased bone formation due to the hypersecretion of thyroid hormones. Any increase in bone turnover, whether focal or diffuse, will result in an increase in Tc-99m- methylenediphosphonate uptake (MDP). The measurement of this uptake in hyperthyroid patients by bone provides a sensitive and objective means of quantifying skeletal metabolism. Using a standard shadow-shield whole-body monitor and radioimmunoassay kit, we have measured whole-body retention of Tc-99m-MDP up to 24hr and concentration of serum Osteocalcin in 20 patients with hyperthyroidism and in 42 normals. The results were as follows; 1) The average of serum Osteocalcin level in 42 patients with normals was 9.90¡¾4.87(ng/ml) and in 20 patients with hyperthyroidism was 19.54¡¾5.7(ng/ml). Both the averages of serum Osteocalcin and 24hr Tc-99m-MDP uptakes in hyperthyroid patients were higher than those in normals. 2) Tc-99m- MDP uptakes in skeletal system increased in proportion to normal ageing after 40 yrs old in 42 patients with normals. The average of Tc-99m-MDP uptakes in hyperthyroid patients were higher than those in normals without related ageing. 3) A significant relationships between the Tc-99m-MDP uptakes and serum Osteocalcin level were peformed (r=0.55, y=17.58+6.7¡¿). From the above results we concluded that the measurement of serum Osteocalcin and 24hr Tc-99m- MDP uptakes can be used for evaluation of bone turnover as a specific marker in hyperthyroid patients.