Juvenile idiopathic arthritis is the most common chronic arthropathy in childhood. According to ILAR criteria JIA is defined as persistent arthritis for more than 6 weeks with an onset at less than 16 years of age. JIA consists of six subtypes. Macrophages, dendritic cells and lymphocytes T are of great importance in pathogenesis of the disease. Prolonged activation of these cells leads to imbalance between concentrations of pro- and anti-inflammatory factors, which sustain inflammatory process. Many researches confirm elevated levels of interleukin 1b, interleukin 6 and tumor necrosis factor in serum and synovial fluid of JIA patients (depending on disease subtype). Evaluation of serum and synovial concentrations of IL-1b, IL-6, TNF-α can make earlier diagnosis of active inflammatory process possible, in case of normal results of other laboratory tests. It will allow to establish earlier diagnosis of JIA and prognosis for future. In addition in some cases it will let to decide on earlier onset of biological treatment.