The pathogenicity of strains of avian influenza virus subtype H5N1 from the Russian Federation (A/turkey/Suzdalka/12/05, A/goose/Krasnoozerskoye/627/05, A/duck/Tuva/01/06, A/chicken/Reshoty/02/06, and A/chicken/Krasnodar/123/060) was studied in mice. Morphological and immunological characteristics of experimental viral infection with avian influenza virus subtype H5N1 were evaluated.