1 . Three species of East African bats were inoculated intraperitoneally with a variety of arboviruses which occur in Uganda. Yellow fever and Bunyamwera viruses circulated in considerable quantity in the fruit bats Eidolon and Rousettus, and also in Tadarida. Zika virus circulated in some of the fruit bats, but not in Tadarida. Sindbis produced demonstrable viraemia in a single Eidolon, while yellow fever (French neurotropic) virus circulated in some of both the species of fruit bat tested.
2 . Ntaya, West Nile, Entebbe bat salivary gland, Usutu and yellow fever (Phlebotomus) viruses did not produce demonstrable viraemia in the fruit bats tested, and in Tadarida Ntaya, yellow fever (Phlebotomus) and Zika viruses gave negative results.
3 . Transmission attempts with two viruses isolated from bats (Entebbe bat salivary gland and Bukalasa bat) in Aedes (Stegomyia) aegypti were not successful, although Entebbe bat salivary gland virus was maintained for 21 days in some of the mosquitoes.
4 . The mechanism of transmission of these viruses from bat to bat is discussed.