The possibility to use agrobacterial transformation of leaf discs to produce resistance to bacterial infections in tobacco and potato plants by introduction of a single gene encoding the serine proteinase inhibitor BWI-1a (ISP) from buckwheat seeds is shown. All studied PCR-positive transgenic plants exhibited antibacterial activity in biotests. It was shown that the presence of just a single gene of serine proteinase inhibitor provides sufficient protection at least against two bacterial phytopathogens, Pseudomonas syringae pv. tomato and Clavibacter michiganensis sbsp. michiganensis. The biotest including tobacco plant infection by the white wings butterfly in the green house has also demonstrated the existence of protective effect in transgenic tobacco plants. Significant genotypic variations in the protection efficiency were found between members of different genera of the same family (potato and tobacco) as well as between different lines of the same species. Northern blot analysis of four transgenic potato lines and three tobacco lines transformed by a vector plasmid containing the ISP gene of serine proteinases BWI-1a from buckwheat seeds has shown the presence of the expected size mRNA transcript.