This paper describes a series of experiments which were done to determine the behavior of 14 different phleboviruses in laboratory-reared sand flies (Phlebotomus papatasi, P. perniciosus and Lutzomyia longipalpis) after oral and parenteral infection. Most of the viruses replicated in the sand flies after intrathoracic inoculation; however, the insects were quite refractory to oral infection. Six of 11 phleboviruses tested were transovarially transmitted in one or more sand fly species. The percentage of infected F1 offspring produced by parenterally infected female parents ranged from 1.5–60%, depending on the virus type used. These data support the hypothesis that some of the phleboviruses are maintained in sand flies by transovarial transmission.