Objectives: Study of circulating and synovial levels of osteocalcin, osteoprotegerin and tumor necrosis factor-alpha (TNF-) in patients with different stages of knee osteoarthritis and correlation analysis of these parameters with disease severity. Methods: We enrolled 20 patients with different stages of knee osteoarthritis. The IKDC score (International Knee Documentation Comittee, 2000) was determined for each patient. Based on these data patients were divided into two groups: group I (advanced osteoarthritis) and group II (early osteoarthritis). Serum and synovial fl uid levels of osteocalcin, osteoprotegerin, TNF- were determined. Results: For the entire group the level of osteocalcin in the serum showed higher values than in the synovial fl uid. We found statistically signifi cant differences in the serum levels of osteocalcin between the two groups (group I: 2.18 ± 0.54 ng/ml, group II: 6.07 ± 1.98 ng/ml, p = 0.019). Serum and synovial osteocalcin in the whole study lot could not be correlated with the disease score, however we observed a tendency towards signifi cant negative correlation between the serum osteocalcin and IKDC score for group I and between synovial osteocalcin and IKDC score in group II. In the entire group, synovial osteoprotegerin concentration was six times higher than the serum osteoprotegerin level (p <0.0001) and TNF- showed higher circulating levels than local concentrations. Conclusions: In the advanced osteoarthritis group the serum and synovial osteocalcin show lower values than in the early osteoarthritis group, which means that as the disease progresses, bone anabolism decreases. In the case of osteoprotegerin, no signifi cant difference between the two groups was detected.