Conjugative transfer of the incompatibility group plasmids Inc P-2, Inc P-3, Inc P-4 and Inc P-5 as well as the plasmids of Pseudomonas sp. of an unknown incompatibility group to the cells of Pseudomonas mallei C-5 was shown possible for the first time. The inheritance of the transferred plasmids and the expression of the markers of resistance to antibacterial drugs were stable. Clones with reserved virulence, lowered virulence and no virulence were detected among the transconjugants. The results of the immunization by the avirulent cells of P. mallei C-5 (RP4) were evident of low immunogenic capacity of the microbe.