Based on current data from domestic and foreign studies, the article presents relevant information on clinical, hematological and biochemical markers of bacterial infection (BI) in children of different ages, which are indications for antibiotic therapy. The article provides criteria for the clinical differential diagnostics of viral, bacterial and severe bacterial infections in children. Clinical and laboratory signs of systemic BI in newborns are described separately. Depending on age, starting from birth, the cut-off values and prognostic potential of leukocytes, neutrophils, C-reactive protein and procalcitonin levels as the most informative laboratory markers of BI are presented. Numerous alternative reasons for increasing the level of these indicators, which justify the need to simultaneously identify several markers are listed. © 2019, Pediatria Ltd.. All rights reserved.