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The coat protein gene (CP) from a highly virulent, necrotic and dominant strain of potato virus Y (PVY) originated from the Hungarian flora has been engineered via Agrobacterium infection into different Hungarian tobacco breeding lines and cultivars. The integration of the CP was confirmed by polymerase chain reaction (PCR) using genomic preparations. The transcription and the expression of the integrated CP gene were detected by Northern and Western analysis. The pathogen-derived resistance was demonstrated by inoculation of the R1 progeny of transformant plants with purified PVY. The efficiency of the protection varied between different transgenic tobaccos ranging from complete to no protection. The challenge infection of the plants was monitored by dot blot hybridisation at different intervals after mechanical inoculation.Western blot analysis showed that there is no correlation between the level of expressed CP and the extent of resistance. From tobacco cultivars namely Virgin D, Stamm C2 and Hevesi 11, 38, 55 and 23 transformants were obtained, respectively. After several years of greenhouse experiments, only the extreme resistant tobaccos were planted field under the special licence, given by the competent authority. In field conditions, transgenic tobacco varieties showed extreme resistance against natural infection of PVY.