For a more comprehensive assessment of the biochemical changes occurring in the course of juvenile idiopathic arthritis, an analysis was also conducted to evaluate the relationships between adiponectin, leptin, and tenascin C concentrations and nonspecific inflammatory markers, namely erythrocyte sedimentation rate (ESR) and C-reactive protein (CRP) in the blood of children with JIA, both untreated and undergoing biological therapy. The gene discussed is TNC; the disease is juvenile idiopathic arthritis.