Osteocalcin (OC) was measured in serum samples from 92 children and adolescents (57 females, 35 males) by a two-site chemiluminescence immunometric assay (Nichols Institute Diagnostics, USA), which recognizes the 1-19 region of the whole molecule as well as the large N-terminal midregion fragment representing the main part of OC in serum. The highest OC levels are measured between the age of 10-15 years. The linear correlations between OC and alkaline phosphatase were 0.65 (p < .01) for total alkaline phosphatase (TAP) and 0.61 (p < 0.1) for bone alkaline phosphatase (BAP).