In the history of the development of virology, two approximately identical in terms of length of periods can be distinguished. The first began with the research of D.I. Ivanovsky and ended with the establishment of a viral etiology of long-known diseases of man, animals, plants, the discovery of bacteriophages and their spread in nature. In this case, the research materials were organs and tissues, their filtrates, secrets and excrements of animals and people, food and feed extracts, water and other factors of transmission of viral infections. The success of solving the tasks in different years of the initial period, of course, was determined by experimental models. So, initially virological studies were carried out on white mice, rats, rabbits and hamsters. Soon, however, a search began for other laboratory animals more susceptible to viruses and work on the development of special lines resistant to bacteria and highly sensitive to viruses obtained at the Rockefeller Institute. The turning point in the rapid development of virology was 1940, when E. Goodpasschur proposed using chicken embryos to isolate viruses from materials, and especially 1949, in which J. Enders, F. Robbins, and T. Weller completed a study on the creation of single-layer cell cultures. that 5 years later they were awarded the Nobel Prize. The second, higher level of developmental period of virology became possible after M. Bories and N. Rusk constructed an electron microscope, the improvement of which allowed in 50-60 years. study in detail the fine structure of viruses, the processes of their replication and assembly of viral particles in cells. It culminated in the greatest discovery that Nobel Laureates X. M. Temin and D. Baltimore made in 1970, isolating reverse transcriptase from retroviruses, which laid the foundation for the development of genetic engineering, the production of biologically active substances and new plant races, recombinant vaccines of the future for preventive medicine, etc.