Osteocalcin is the major noncollagenous protein of the bone matrix and has been described as a sensitive marker reflecting bone turn-over rate. It's believed to play a role in the process of mineralization. The level of osteocalcin is considered to be influenced by other calcium regulating hormones. To obtain the normal value of osteocalcin in Korean young adults and to clarify the usefulness of osteocalcin as a marker reflecting bone turn-over in suspicious disuse-osteporotic patient, author measured the level of osteocalcin by radioimmunoassay. The results are; 1. The mean circulation osteocalcin level in healthy young adults was 4.43+ 1.09ng/ml. 2. In normal Korean male, the serum osteocalcin level was 4.38±1.16ng/ml and in normal Korean female, 4.48±1.02ng/ml. There was no significant difference in both sexes, but the serum osteocalcin level in female reveals some tendency of elevation when compared with male. 3. In suspicious disuse-osteoporotic patients, the mean serum osteocalcin level was 4.21±1.30ng/ml and this result shows no difference from that of normal young adults. 4. The level of osteocalcin measured in the normal young Korean adults shows no difference from the prerecorded INC level measured in the Western people. 5. In conclusion, the normal value of osteocalcin in normal young Korean adults is similar that of western people, and the measurement of osteocalcin in suspicious disuse-osteoporotic patients could not be used as a sensitive marker reflecting bone turn-over.