T-DNA insertion mutagenesis, a novel molecular-genetic approach, was used to obtain tomato (Lycopersicon esculentum Mill.) plants resistant to late-blight disease caused by Phytophthora infestans (Mont.) De Bary. Plants were inoculated with a mixed pathogen population combining isolates from several sites in the Leningrad oblast. Among the plants of the primary transformant and first generation, we discerned forms with a modified leaf pattern and relative resistance to late blight. The plants with the modified leaf pattern were sterile: their bud initials never developed into flowers. The resistant plants were obtained at a frequency of 0.1%.