As a result of accelerated osteoclastic and osteoblastic activities in hyperthyroid state, loss of bone mass occurs. Osteocalcin levels were investigated in Graves' disease and euthyroid individuals. Average serum osteocalcin levels were found to be 13.3±4.3 ng/ml and 7.6±2.4 ng/ml for the Graves' and the euthyroid group respectively. Serum osteocalcin appears to be a sensitive marker of hyperthyroid osteopathy and more suitable and precise than the usual markers of bone metabolism.