The mechanisms of pianl resistance to pathogens and pests are reviewed. The data on the molecular structure of the plant R genes, signal molecules, the induction of hypersensitive response (HR), and systemic acquired resistance (SAR.) to diseases are presented. Special attention is given to one of the main resistance mechanisms against recent blights-the transition from sterol biosynthetic pathways to the production of phytoalexins. The role of plant sterols in the development of phytosterol-dependent pests is demonstrated. The data concerning sterol biosynthesis in plant cells and their functions are given. Sterol mutants and their induction are described. The authors suggest the use of natural plant-pest relationships for producing resistant plants. The results, which deal with the generation of potatoes resistant to recent blights using cell-selection methods with plant selection for resistance to polyene antibiotics and inhibitors of sterol biosynthesis, are presented. It is suggested to use this approach, which exploits the natural phytosterol dependence of many pathogens, as a new biological measure against crop pests.