Objective: to determine the urinary concentrations of cytokines for the diagnosis of the localization of inflammation in the urinary system and to establish the contribution of mediators of the immune system to the pathogenesis of the pathology in question. Twenty-nine children aged 2.7 to 11.5 years with pyelonephritis (n=16) and the unspecified localization of urinary infection or cystitis (n=13) were examined. A control group consisted of 15 healthy children. Cytokine levels were determined in the morning urine portion using the multiplex xMAP technology and then recalculated to the concentration of creatinine. Urinary tract infection was accompanied by an avalanche-like increase in the total urinary cytokine concentration, which was 20-fold greater than the reference values in the children with pyelonephritis. Interleukin 8 (IL-8) constituted the highest proportion of cytokines. IL-10 and interferon-γ (IFN-γ) made up the smallest percentage in the total mass of cytokines. Higher IL-6 and IFN-γ values and a simultaneous increase in the level of 2 or more cytokines are of the greatest diagnostic value in determining the renal site of urinary tract infection.