The effectiveness of specific phage therapy was studied on Klebsiella experimental sepsis in noninbred white mice, caused by the intraperitoneal injection of K. pneumoniae highly virulent strain K2 5055 into the animals. For treatment, Klebsiella polyvalent bacteriophage administered on day 2 after the infection of the animals with Klebsiella was used. The study revealed that bacteriophage could be detected in the blood and internal organs of the animals within 24 hours irrespective of the route of its administration: intraperitoneal, intravenous or intranasal. The bacteriophage preparation, introduced intraperitoneally, was shown to be effective in the treatment of generalized Klebsiella infection. One daily intraperitoneal injection of Klebsiella bacteriophage for 15-20 days proved to be the optimum scheme of treatment. In contrast to chemotherapeutic preparations, bacteriophages had no effect on normal microflora and did not aggravate dysbiotic disturbances. For this reason, bacteriophages may become one of alternative antimicrobial remedies, selectively affecting infective agents.