Clinical utility of biochemical bone turnover markers in children and adolescents with osteosarcoma. Biochemical markers of bone turnover reflecting the intensity of all bone remodeling processes in skeleton are important for fast and non-invasive assessment of bone formation and resorption processes. They can be used in terms of both physiological and pathological states. The aim of this study was to investigate if bone metabolism markers can be clinically useful for monitoring of treatment in children and adolescents with osteosarcoma.The study consisted of 55 patients (median age 15 years) with osteosarcoma and 60 healthy age matched counterparts. Serum bone turnover markers (bone alkaline phosphatase - BALP, osteocalcin - OC and C-terminal telopeptide of type I collagen - CTX) were analyzed by immunoenzymatic methods in patients at time of diagnosis, during treatment and after therapy.We observed that before treatment the concentration of OC in patients with osteosarcoma was significantly lower (p<0.05) compared to that obtained in healthy children, however, BALP and CTX were at a similar level. During chemotherapy the values of bone formation and resorption markers significantly decreased by about 20-30%. After therapy we observed different concentrations of all bone turnover markers in patients with favorable and unfavorable prognosis. Median values of OC and BALP were over twofold higher in patients with progression as compared to patients with remission of disease (p<0.01 and p<0.001, respectively). Patients with poor prognosis had also higher serum concentration of bone resorption marker in comparison to patients with remission (p<0.01).Presented results suggest that bone turnover markers identify changes in bone metabolism in patients with osteosarcoma during anticancer therapy. These markers due to the non-invasive methods and their specificity might be useful in monitoring of clinical treatment of osteosarcoma patients.