The clinical and laboratory study of 190 hospitalized children revealed that in 122 cases the course of the underlying disease was complicated by Klebsiella infection. From different pathological material obtained from 122 patients 158 K. pneumoniae cultures were isolated. These cultures were mostly isolated from the respiratory organs (69%), from patients with the generalized infection (21.6%), and less frequently from operative wounds and burn surfaces (5.8%), the gastrointestinal tract (1.4%) and the urinary system (1.4%). The isolated clinical strains were multiresistant to antibiotics and contained plasmid DNA with molecular weights of 70 and 105 MD (60.4%). K. pneumoniae were shown to produce an aggravating effect on the course and outcome of the underlying disease, mainly in preterm babies or those born asphyxiated or with congenital defects of development, as well as in patients with immunodeficient states. The probability of infection was directly related to the character and number of medical manipulations on an infant, mainly in connection with artificial ventilation of the lungs and transfusion therapy.