A total of 67 patients with diseases of the blood system and infectious complications, admitted to the Hematological Department of the Novosibirsk Regional Clinical Hospital, were examined. For this study only patients with etiologically established diagnosis were taken. The study revealed that Pseudomonas sp., whose strains were susceptible to Ceftazidime in 100% of cases and resistant to Cefepime and Imipenem in 15-17% of cases, was the etiological agent of 13.6% of all cases of infectious complications in hemoblastosis patients. Infectious lesions of pulmonary parenchyma, the presence of chronic diseases of the respiratory tract in the medical history, neutropenia, artificial ventilation of the lungs were found to be adverse prognostic factors with respect to a high risk of Pseudomonas infection in such patients. Therapy with glucocorticosteroids and cytostatics, preceding antibacterial prophylaxis were not linked with the isolation of Pseudomonas from the patients exhibiting the same levels of lethality and severity of infectious complications.