While comparatively analyzing the properties of Klebsiella pneumoniae from three studied sources (patients, healthy people, environment), no reliable differences between the comparable strains have been revealed. No differences have been found in the toxin formation, hemagglutinating and antilysozymic activity, adhesivity and invasive properties as well as in the peculiarities of gas exchange, while growing on media with different nitrogen and carbon sources. The studied microorganisms differed only in antibiotic resistance: strains isolated from the environment were sensitive to antibiotics, whereas strains of human origin were resistant to them.