A method was developed for detection of group A arboviruses, Sindbis and Venezuelan equine encephalomyelitis (VEE), in the salivary glands of experimentally infected Aedes aegypti mosquitoes by direct immunofluorescence with counter staining. During the period shortly after infection, the virus was localized in distal parts of the lateral lobules of the salivary glands, whereas during the time of maximum multiplication it was concentrated in the anterior parts. Detection of the virus in the salivary glands by immunofluorescent staining techniques reflected the ability of the mosquito to transmit infection by bite.