Poliomyelitis viruses were successfully used to produce plaques on monolayer cultures of monkey kidney cells, enabling the study of virus-host cell interactions similar to those in bacteriophage research. These viruses, known for their stability, growth in tissue culture, and cytopathogenicity, also exhibit genetic variability, making them suitable for genetic studies. Plaques formed by these viruses can be efficiently used for titration, and pure viral lines can be isolated from individual plaques. High-titer virus stocks were obtained during this work. The study involved preparing tissue cultures from cynomolgus monkey kidney or testis, which were then infected with poliomyelitis viruses. Plaques formed on the cultures were used to isolate pure viral lines. The number of plaques was proportional to the virus concentration, and each plaque originated from a single virus particle, termed the virus unit. Plaques were suppressed by type-specific antiserum, indicating their specific viral origin. The plaque technique provided a sensitive and reproducible method for virus titration and isolation of pure viral lines. The technique was validated by experiments showing that plaques were due to the specific action of the virus and that the number of plaques was closely reproducible and proportional to the virus concentration. The method was more sensitive than traditional titration methods. The study also demonstrated that a single virus particle was sufficient to infect a cell, as evidenced by the linear relationship between plaque number and virus concentration. This finding supports the idea that a single virus particle is sufficient to initiate infection. The plaque-forming dose contains at least one plaque-forming particle, and the technique allows for the isolation of pure viral lines. The production of high-titer virus stocks was achieved by infecting cultures with sufficient virus to infect almost every cell, resulting in titers up to 7 × 10⁸ plaque-forming particles per ml. The study also showed that the plaque-forming titer of a virus stock was similar to its monkey-infectious titer, indicating that a single virus particle is sufficient to infect a monkey. The results of this study have significant implications for the study of viral genetics and the development of viral vaccines. The plaque technique provides a reliable method for virus isolation and titration, and the ability to isolate pure viral lines is crucial for understanding viral properties and for vaccine development. The study also highlights the importance of understanding the mechanisms of viral infection and the factors that influence viral replication and spread.Poliomyelitis viruses were successfully used to produce plaques on monolayer cultures of monkey kidney cells, enabling the study of virus-host cell interactions similar to those in bacteriophage research. These viruses, known for their stability, growth in tissue culture, and cytopathogenicity, also exhibit genetic variability, making them suitable for genetic studies. Plaques formed by these viruses can be efficiently used for titration, and pure viral lines can be isolated from individual plaques. High-titer virus stocks were obtained during this work. The study involved preparing tissue cultures from cynomolgus monkey kidney or testis, which were then infected with poliomyelitis viruses. Plaques formed on the cultures were used to isolate pure viral lines. The number of plaques was proportional to the virus concentration, and each plaque originated from a single virus particle, termed the virus unit. Plaques were suppressed by type-specific antiserum, indicating their specific viral origin. The plaque technique provided a sensitive and reproducible method for virus titration and isolation of pure viral lines. The technique was validated by experiments showing that plaques were due to the specific action of the virus and that the number of plaques was closely reproducible and proportional to the virus concentration. The method was more sensitive than traditional titration methods. The study also demonstrated that a single virus particle was sufficient to infect a cell, as evidenced by the linear relationship between plaque number and virus concentration. This finding supports the idea that a single virus particle is sufficient to initiate infection. The plaque-forming dose contains at least one plaque-forming particle, and the technique allows for the isolation of pure viral lines. The production of high-titer virus stocks was achieved by infecting cultures with sufficient virus to infect almost every cell, resulting in titers up to 7 × 10⁸ plaque-forming particles per ml. The study also showed that the plaque-forming titer of a virus stock was similar to its monkey-infectious titer, indicating that a single virus particle is sufficient to infect a monkey. The results of this study have significant implications for the study of viral genetics and the development of viral vaccines. The plaque technique provides a reliable method for virus isolation and titration, and the ability to isolate pure viral lines is crucial for understanding viral properties and for vaccine development. The study also highlights the importance of understanding the mechanisms of viral infection and the factors that influence viral replication and spread.