In the present paper the author describes the experiments made by the inoculation of PR8 strain of influenza virus (routine passages 669 to 825 in mice) in hamsters by subcutaneous, peritoneal and nasal routes and also passages from inoculated hamster to normal hamsters in serial passages. The virus persisted at least until 515 days in one experiment (3rd). In another experiment (8th) the 9th passage was positive. The hamsters inoculated did not show signs of illness or lesions macroscopic of microscopic in the main organs after death.